[PATCH 0/2] Add ipv4 if addr hash.

These changes are based upon something I brought up the other day,
namely that we do a full FIB lookup just to find whether a particular
unicast ipv4 address is attached to an interface.

Like ipv6, I added an RCU/RTNL protected hash table and reimplemented
__ip_dev_find() in terms of it.

These patches apply both with and without the route cache deletion
patch applied, but with the route cache removal applied the udpflood
test gets faster by ~13 seconds:

real	2m57.500s
user	0m10.640s
sys	2m46.910s

We can probably use this new table for other things as well.