net: don't bind on 0.0.0.0 if binds are restricted to Tor

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.

test/functional/test_runner.py

@@ -138,6 +138,7 @@ BASE_SCRIPTS = [
     'interface_zmq.py',
     'rpc_invalid_address_message.py',
     'interface_bitcoin_cli.py',
+    'feature_bind_extra.py',
     'mempool_resurrect.py',
     'wallet_txn_doublespend.py --mineblock',
     'tool_wallet.py --legacy-wallet',