Instead of requiring a run with an explicit `--ihave1111and2222`, detect
whether the routable addresses are set up and if not, then skip the test.
To detect whether the addresses are set use `bitcoind` - start it
and ask it to bind on them and see if it will error with
"Unable to bind". Since this is what the tests do anyway, just start
the nodes and see if an exception will be raised like
`FailedToStartError` / "Unable to bind".
This makes it possible for the CI to run
`feature_bind_port_discover.py` and
`feature_bind_port_externalip.py` by just setting up the
addresses, without having to explicitly provide `--ihave1111and2222`.
Co-authored-by: willcl-ark <will@256k1.dev>
`GetListenPort()` uses a simple logic: "if `-port=P` is given, then we
must be listening on `P`, otherwise we must be listening on `8333`".
This is however not true if `-bind=` has been provided with `:port` part
or if `-whitebind=` has been provided. Thus, extend `GetListenPort()` to
return the port from `-bind=` or `-whitebind=`, if any.
Fixes https://github.com/bitcoin/bitcoin/issues/20184 (cases 1. 2. 3. 5.)
