[PATCH 0/4] More rt->rt_dst whittling...

After this patch series all of the real references to rt->rt_dst that
remain are having to do with inetpeer lookups.

Already, rt->rt_src has no fundamental references any longer, and with
the routing cache it can be safely removed.

The last step of detaching the final rt->rt_dst uses will need a little
bit of work, because we currently don't propagate the originating
lookup flow key into the various dst_ops such as ->cow_metrics,
->default_mtu, etc. and those do PEER lookups which need the destination
address in use.