When rtcp listener calls Router.Bind with ":8000" (port-only address),
the relay AddrFeature.ParseFrom fails because net.SplitHostPort returns
an empty host. This leaves AType at default 0, causing AddrFeature.Encode
to return ErrBadAddrType.
Fix by normalizing port-only addresses to "0.0.0.0:<port>" in both tunnel
and relay connectors before ParseFrom. Also fix error check on
resp.WriteTo in the tunnel handler's handleBind to prevent silent
protocol desync.
ginuerzh