The semantic of -bind is to restrict the binding only to some address.
If not specified, then the user does not care and we bind to 0.0.0.0.
If specified then we should honor the restriction and bind only to the
specified address.
Before this change, if no -bind is given then we would bind to
0.0.0.0:8333 and to 127.0.0.1:8334 (incoming Tor) which is ok -
the user does not care to restrict the binding.
However, if only -bind=addr:port=onion is given (without ordinary
-bind=) then we would bind to addr:port and to 0.0.0.0:8333 in
addition.
Change the above to not do the additional bind: if only
-bind=addr:port=onion is given (without ordinary -bind=) then bind
to addr:port (only) and consider incoming connections to that as Tor
and do not advertise it. I.e. a Tor-only node.