add optional simulated addresses to pipeconn and inmemorylistener

[tobikris]

I have a use case where I need the code using this InmemoryListener to access the simulated address of the connection endpoints.
This PR adds optional addresses to the PipeConns and InmemoryListener.
If the feature is not used, the code behaves like before.

Example:

func main() {
	ln := NewInmemoryListener()

	listenerAddr := &net.TCPAddr{IP: net.IPv4(127, 0, 0, 1), Port: 12345}

	ln.SetLocalAddr(listenerAddr)

	go client(ln)

	lc, err := ln.Accept()
	if err != nil {
		log.Fatalf("unexpected error: %v", err)
	}

	log.Println(lc.LocalAddr(), lc.RemoteAddr())
}

func client(ln *InmemoryListener) {
	clientAddr := &net.TCPAddr{IP: net.IPv4(127, 0, 0, 2), Port: 65432}

	c, err := ln.DialWithLocalAddr(clientAddr)
	if err != nil {
		log.Fatalf("unexpected error: %v", err)
	}

	log.Println(c.LocalAddr(), c.RemoteAddr())
}

[li-jin-gou]

Do SetLocalAddr() and Addr() need to be considered for concurrency?

[tobikris]

You could argue that it needs to be. However, I thought the only meaningful way to set the address would be to do it before the listener is used in any way. I just did not add it to NewInmemoryListener() to leave this completely optional.

It is probably better to guard against data races, though, and to do not leave this to the caller. I will implement it, thanks!

[erikdubbelboer]

Thanks!