addrmgr: Expose method to update services.

This exposes a new method named SetServices to the address manager which
can be used to update the services for a known address.  This will be
useful to keep known services up to date.

Backported from Decred.

addrmgr/addrmanager.go

@@ -1,4 +1,5 @@
 // Copyright (c) 2013-2016 The btcsuite developers
+// Copyright (c) 2015-2018 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -937,6 +938,25 @@ func (a *AddrManager) Good(addr *wire.NetAddress) {
 	a.addrNew[newBucket][rmkey] = rmka
 }
 
+// SetServices sets the services for the giiven address to the provided value.
+func (a *AddrManager) SetServices(addr *wire.NetAddress, services wire.ServiceFlag) {
+	a.mtx.Lock()
+	defer a.mtx.Unlock()
+
+	ka := a.find(addr)
+	if ka == nil {
+		return
+	}
+
+	// Update the services if needed.
+	if ka.na.Services != services {
+		// ka.na is immutable, so replace it.
+		naCopy := *ka.na
+		naCopy.Services = services
+		ka.na = &naCopy
+	}
+}
+
 // AddLocalAddress adds na to the list of known local addresses to advertise
 // with the given priority.
 func (a *AddrManager) AddLocalAddress(na *wire.NetAddress, priority AddressPriority) error {