Fix forwarning of node RPC responses to the registry

This is another regression with the migration to Python 3, causing here
the registry to return invalid addresses to bootstrapping nodes and
then socket.gaierror exceptions.

re6st/tunnel.py

@@ -465,7 +465,8 @@ class BaseTunnelManager:
         code = c & 0x7f
         if c > 0x7f and msg:
             if peer and self._forward:
-                self._sendto(self._forward, '%s\0%c%s' % (peer, code, msg))
+                self._sendto(self._forward,
+                             b'%s\0%c%s' % (peer.encode(), code, msg))
         elif code == 1: # address
             if msg:
                 if peer: