svc/conntrack.in: Force reconnection on local IP address changes.

ICd or NetworkManager might roam to a new network, and tell us about it;
but if we decided that we wanted to stick with the same peer
specification then our peer will continue with the wrong IP address until
watch gets a ping timeout.

Of course, this doesn't trap other reasons we might change IP addresses
without anyone noticing, such as roaming to a different 3G NAT thingummy.