migration: Add migration_incoming_transport_cleanup()

migration: Add migration_incoming_transport_cleanup()

Add a helper to cleanup the transport listener.

When do it, we should also null-ify the cleanup hook and the data, then it's
even safe to call it multiple times.

Move the socket_address_list cleanup altogether, because that's a mirror of the
listener channels and only for the purpose of query-migrate.  Hence when
someone wants to cleanup the listener transport, it should also want to cleanup
the socket list too, always.

No functional change intended.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20220301083925.33483-15-peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>