Add if_reassign method to all tunneling interfaces.

After r339550 tunneling interfaces have started handle appearing and
disappearing of ingress IP address on the host system.
When such interfaces are moving into VNET jail, they lose ability to
properly handle ifaddr_event_ext event. And this leads to need to
reconfigure tunnel to make it working again.

Since moving an interface into VNET jail leads to removing of all IP
addresses, it looks consistent, that tunnel configuration should also
be cleared. This is what will do if_reassign method.

Reported by:	John W. O'Brien <john saltant com>