WIP: relay: Publish IPv4 descriptor on guessed IPv6 reachability failure

On an IPv6 reachability failure test, if the address was configured, don't publish the descriptor and log warn.

If the address was auto discovered, still publish the descriptor.

To achieve the above, this adds a "last address configured" cache so we can track which address family last was found configured or not.

Closes #33247 (closed).

Signed-off-by: David Goulet dgoulet@torproject.org