IFNET/IFADDR statistics are now per-CPU

[Sepherosa Ziehau]

Hi all,

As of e1fcdad72cfb9eab8f4873e5b9330f2a753dfefa, IFNET/IFADDR stats are
per-CPU and their locations are changed.  It greatly improves stats
accuracy (especially for high rate small packets); should be useful
for user space programs to perform network load balance.

- Callers of sysctl IFMIB_IFDATA are _not_ affected.
- For programs that directly access ifnet.if_data and ifaddr.if_data
to get statistics, they need to be _modified_ to use the new stats
location.  /usr/src/usr.bin/netstat/if.c could be used as example.

Best Regards,
sephe

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