Add stub/wrapper for reuseport.Listen on Windows platforms

[andrewheberle]

This PR adds a "stub" Listen function for Windows only that always returns (*reuseport.ErrNoReusePort) so the same code can be used on Windows and non-Windows platforms.

So in this case the following code will work on Windows as well as Linux/BSD platforms

// create server
srv := fasthttp.Server{
	Handler:      requestHandler,
	ReadTimeout:  5 * time.Second,
	WriteTimeout: 10 * time.Second,
	IdleTimeout:  120 * time.Second,
}

// try using SO_REUSEPORT
nl, err := reuseport.Listen(addrFamily, listenAddress)
if err != nil {
	if _, noreuseport := err.(*reuseport.ErrNoReusePort); noreuseport {
		// fall back to plain net.Listen
		nl, err = net.Listen(addrFamily, listenAddress)
		if err != nil {
			fmt.Printf("Error: %s\n", err)
			os.Exit(1)
		}
	} else {
		fmt.Printf("Error: %s\n", err)
		os.Exit(1)
	}
}

// run server
if err := srv.Serve(nl); err != nil {
	fmt.Printf("Error: %s\n", err)
}

[erikdubbelboer]

Are you 100% sure this is required. This pull request here says it's not needed in Go 1.12 anymore: valyala/tcplisten#2

[andrewheberle]

Are you 100% sure this is required. This pull request here says it's not needed in Go 1.12 anymore: valyala/tcplisten#2

I saw that however I don't know what that comment is based on as the Go 1.12 release notes don't mention any new support/changes in "net" that could make this work now and my Windows Go 1.12 install fails the same way as noted in that PR.

[erikdubbelboer]

Sorry, 2 last modifications and then this can be merged.

[erikdubbelboer]

Thanks!