multi: Added a NetInterface to clean up config.go

This commit adds a new interface named NetInterface and two
implementations of it: RegularNet & TorProxyNet. These two structs
are used in config.go in an attempt to clean up the code and
abstract away the dialer and DNS functions.

rpcserver.go

@@ -590,7 +590,7 @@ func (r *rpcServer) ConnectPeer(ctx context.Context,
 	}
 
 	// We use lndResolveTCP here in case we wish to resolve hosts over Tor.
-	host, err := lndResolveTCP("tcp", addr)
+	host, err := cfg.net.ResolveTCPAddr("tcp", addr)
 	if err != nil {
 		return nil, err
 	}