Do not change the interface of a route if it is not intended.
Do not change the interface of a route if it is not intended.

When a route change message is submitted, looks for a new ifa to attach
the route only if a gateway, an ifp or an ifa has been specified.

Fix a regression reported by Florian Riehm, ok bluhm@.

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars