Concurrent map writes panic

[nkryuchkov]

Describe the bug
Sometimes visor panics on shutdown with fatal error: concurrent map writes

Environment information:

• The issue does not depend on the environment.

Steps to Reproduce
Steps to reproduce the behavior:

1. Run visor
2. Press Ctrl-C at a certain moment

Actual behavior
Visor panics

Expected behavior
Visor does not panic

Additional context

[2020-09-09T21:26:03+03:00] INFO [snet.dmsgC]: Cleanly stopped serving. dmsgpty="host" error="dmsg error 200 - local entity closed"
[2020-09-09T21:26:03+03:00] INFO [4/11] [visor:shutdown:dmsgpty.serve]: Module stopped cleanly. elapsed=456.379µs 
[2020-09-09T21:26:03+03:00] INFO [3/11] [visor:shutdown:snet.dmsgctrl]: Shutting down module...                                                                                                                                      
[2020-09-09T21:26:03+03:00] INFO [3/11] [visor:shutdown:snet.dmsgctrl]: Module stopped cleanly. elapsed=21.254µs                                                                                                                     
[2020-09-09T21:26:03+03:00] INFO [2/11] [visor:shutdown:snet]: Shutting down module...                                                                                                                                               
fatal error: concurrent map writes                                                                                                                                                                                                   
[2020-09-09T21:26:03+03:00] INFO [snet.dmsgC]: Stopped serving client!                                                                                                                                                               
                                                                                                                                                                                                                                     
goroutine 273 [running]:                                                                                          
runtime.throw(0x1a23510, 0x15)                                                                                                                                                                                                       
        /usr/local/Cellar/go/1.14.5/libexec/src/runtime/panic.go:1116 +0x72 fp=0xc0005a7710 sp=0xc0005a76e0 pc=0x1033eb2                                                 
runtime.mapassign_faststr(0x18e3ae0, 0xc000203200, 0x1a15c90, 0x5, 0xc00009ae70)                                                                                                                                                     
        /usr/local/Cellar/go/1.14.5/libexec/src/runtime/map_faststr.go:211 +0x3f7 fp=0xc0005a7778 sp=0xc0005a7710 pc=0x10132f7                                               
github.com/skycoin/skywire/pkg/snet.(*Network).Close.func2(0xc00026cb50, 0xc000203200, 0xc00026cb40, 0xc000496594)                                                        
        /Users/nkryuchkov/GolandProjects/skywire/pkg/snet/network.go:308 +0x7b fp=0xc0005a77c0 sp=0xc0005a7778 pc=0x161c71b
runtime.goexit()                                                                                                                                                                                                                     
        /usr/local/Cellar/go/1.14.5/libexec/src/runtime/asm_amd64.s:1373 +0x1 fp=0xc0005a77c8 sp=0xc0005a77c0 pc=0x1066771            
created by github.com/skycoin/skywire/pkg/snet.(*Network).Close                                                   
        /Users/nkryuchkov/GolandProjects/skywire/pkg/snet/network.go:307 +0x24f                                                                                                                                                      
                                                                                                                  
goroutine 1 [select]:                                                                                                                                                                                                                
github.com/skycoin/skywire/pkg/visor.(*Visor).Close(0xc000151040, 0x0, 0x1b7e380)                                                                                                                                                    
        /Users/nkryuchkov/GolandProjects/skywire/pkg/visor/visor.go:198 +0x568                                    
github.com/skycoin/skywire/cmd/skywire-visor/commands.glob..func1(0x22eb220, 0xc000148380, 0x0, 0x4)              
        /Users/nkryuchkov/GolandProjects/skywire/cmd/skywire-visor/commands/root.go:121 +0x56d                                                                                                                                       
github.com/spf13/cobra.(*Command).execute(0x22eb220, 0xc00019a010, 0x4, 0x4, 0x22eb220, 0xc00019a010)                                                                                                                                
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/spf13/cobra/command.go:846 +0x29d              
github.com/spf13/cobra.(*Command).ExecuteC(0x22eb220, 0x10431ba, 0x2173060, 0xc00005a778)                         
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/spf13/cobra/command.go:950 +0x349
github.com/spf13/cobra.(*Command).Execute(...)                                                                    
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/spf13/cobra/command.go:887                     
github.com/skycoin/skywire/cmd/skywire-visor/commands.Execute()                                                   
        /Users/nkryuchkov/GolandProjects/skywire/cmd/skywire-visor/commands/root.go:130 +0x31                                                                                                                                        
main.main()                                                                                                                                                                                                                          
        /Users/nkryuchkov/GolandProjects/skywire/cmd/skywire-visor/skywire-visor.go:11 +0x20                      
                                                                                                                                                                                                                                     
goroutine 7 [select, 2 minutes]:                                                                                                                                                                                                     
github.com/xtaci/kcp-go.(*Listener).AcceptKCP(0xc000388630, 0x0, 0xc00010e8a0, 0x0)                                                                                                                                                  
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/xtaci/kcp-go/sess.go:900 +0x19a   
github.com/xtaci/kcp-go.(*Listener).Accept(0xc000388630, 0x0, 0x0, 0x0, 0x0)                                   
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/xtaci/kcp-go/sess.go:890 +0x2b      
github.com/skycoin/skywire/pkg/snet/directtp.(*client).acceptConn(0xc000390500, 0x1a23732, 0x15)         
        /Users/nkryuchkov/GolandProjects/skywire/pkg/snet/directtp/client.go:186 +0x6e                            
github.com/skycoin/skywire/pkg/snet/directtp.(*client).Serve.func1(0xc000390500)                                                                                                                                                     
        /Users/nkryuchkov/GolandProjects/skywire/pkg/snet/directtp/client.go:142 +0x197                           
created by github.com/skycoin/skywire/pkg/snet/directtp.(*client).Serve                                                                                                                                                              
        /Users/nkryuchkov/GolandProjects/skywire/pkg/snet/directtp/client.go:115 +0x62                                                                                                                                               
                                                                                                                                                                                                                                     
goroutine 12 [select]:                                                                                            
github.com/xtaci/kcp-go.(*UDPSession).updater(0xc000328000)                                                       
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/xtaci/kcp-go/sess.go:585 +0xe2                                                                                                                                    
created by github.com/xtaci/kcp-go.newUDPSession                                                                                                                                                                                     
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/xtaci/kcp-go/sess.go:185 +0x4e9                
                                                                                                                                                                                                                                     
goroutine 11 [runnable]:                                                                                          
runtime.Callers(...)                                                                                                                                                                                                                 
        /usr/local/Cellar/go/1.14.5/libexec/src/runtime/extern.go:215                                                                                                                                                                
github.com/pkg/errors.callers(0xc0000402c0)                                                                                                                                                                                          
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/pkg/errors/stack.go:136 +0x5b                                                                                                                                     
github.com/pkg/errors.WithStack(...)                                                                              
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/pkg/errors/errors.go:151                       
github.com/xtaci/kcp-go.(*UDPSession).defaultReadLoop(0xc000328000)                                               
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/xtaci/kcp-go/readloop.go:28 +0x1fc             
github.com/xtaci/kcp-go.(*UDPSession).readLoop(0xc000328000)                                                                                                                                                                         
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/xtaci/kcp-go/readloop_generic.go:6 +0x2b
created by github.com/xtaci/kcp-go.newUDPSession                                                                                                                                                                                     
        /Users/nkryuchkov/GolandProjects/skywire/vendor/github.com/xtaci/kcp-go/sess.go:178 +0x552  

Possible implementation
Add a mutex to map