IKEv1 host-to-host with NAT and XAUTH

ikev2-hostpair-01 reconnects using a different pre-NAT IP so it gets
a different port on the NAT router. This emulates switching network
without notify. It should cause east to REPLACE the connection and
get the same IP address back.

On 3.23, this gives "cannot route -- route already in use" error,
and traffic flow stops