Validate address more carefully when checking self-reachability

Previously, we would treat *any* incoming circuit on a non-local
channel as meaning that our ORPort was reachable.  With this patch,
we make sure that the address that the peer _says_ we have is the
same as the one we're trying to advertise right now.

Closes 20165. Bugfix on 4f5192b2 in 0.1.0.1-rc, when
reachability self-tests were first introduced.