- Utilize counter(9) to accumulate statistics on interface addresses. Add
  four counters to struct ifaddr. This kills '+=' on a variables shared
  between processors for every packet.
- Nuke struct if_data from struct ifaddr.
- In ip_input() do not put a reference on ifaddr, instead update statistics
  right now in place and do IN_IFADDR_RUNLOCK(). These removes atomic(9)
  for every packet. [1]
- To properly support NET_RT_IFLISTL sysctl used by getifaddrs(3), in
  rtsock.c fill if_data fields using counter_u64_fetch().
- Accidentially fix bug in COMPAT_32 version of NET_RT_IFLISTL, which
  took if_data not from the ifaddr, but from ifaddr's ifnet. [2]

Submitted by:	melifaro [1], pluknet[2]
Sponsored by:	Netflix
Sponsored by:	Nginx, Inc.