Always call rt_ifa_dellocal(9) when removing an IPv6 address.

Always call rt_ifa_dellocal(9) when removing an IPv6 address.

The routing layer already check for the correct ifa when asked
to delete a local route, so do not try to be clever here.

This change also prevent having a NULL ifp pointer in your routing
table when you delete loopback interfaces having the same address.

ok henning@