- Provide if_get_counter() method for vtnet(4).
- Do not accumulate statistics on every tick.
- Accumulate statistics in vtnet_setup_stat_sysctl()
  and in vtnet_get_counter().

Sponsored by:	Netflix
Sponsored by:	Nginx, Inc.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271799 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f