MFC 212902:

MFC 212902:
Tweak the stats exported by the e1000 drivers:
- Add a single sysctl procedure to all three drivers to read an arbitrary
  register (the register is passed as arg2).  Use it to replace existing
  routines in igb(4) that used a separate routine for each register, and
  to add support for missing stats in em(4) and lem(4).
- Move the 'rx_overruns' and 'watchdog_timeouts' stats out of the MAC stats
  section as they are driver stats, not MAC counters.
- Simplify the code that creates per-queue stats in igb(4) to use a single
  loop and remove duplicated code.
- Properly read all 64 bits of the 'good octets received/transmitted' in
  em(4) and lem(4).
- Actually read the interrupt count registers in em(4), and drop the
  'host to card' sysctl stats from em(4) as they are not implemented in
  any of the hardware this driver supports.
- Restore several stats to em(4) that were lost in the earlier stats
  conversion including per-queue stats.
- Export several MAC stats in em(4) that were exported in igb(4) but not
  in em(4).
- Export stats in lem(4) using individual sysctls as in em(4) and igb(4).

git-svn-id: svn://svn.freebsd.org/base/stable/8@213205 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f