Allow multiple connected/interface routes to exist at the same time.

Allow multiple connected/interface routes to exist at the same time.
Use the existing multipath code. Switch away from using the ifa address
when making the cloning route and instead put a dummy sockaddr_dl route
in. With this it is possible to use the same network on multiple interfaces
at the same time. So if wireless and ethernet share the same network
the system will use the wired connection as long as there is link.
Still missing is builtin proxy-arp for the other interface IPs to allow
hitless failover.
OK mpi@