- Provide igb_get_counter() to return counters that are not collected,
  but taken from hardware.
- Mechanically convert to if_inc_counter() the rest of counters.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271870 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f