Sync re(4) with FreeBSD:

Sync re(4) with FreeBSD:
- Add support for RealTek 8169SC/8110SC and RTL8101E devices.  The latter
  is a PCIe 10/100 chip.
- Add support for RealTek RTL8168(B?)
- Fix EEPROM reading code
- Disable diagnostic code in re_attach() by default.  It is almost useless
  and has caused much trouble.
- Manually padding small IP datagrams to work arround hardware checksum
  offload bug [1].  Enable IP/TCP/UDP checksum offload after this fix.
- Work arround hardware TX bug in some PCIe re(4) devices:
  The TX command, which is issued when there is transmission in progress,
  will get lost [2].
  So at the end of re_txeof(), if there are still packets sitting in the
  TX ring, we kick the TX engine again.
- Add a sysctl hw.reX.tx_moderation to turn on/off TX moderation.  It is
  on by default.
- Move softc related structs from if_rereg.h into newly created if_revar.h

Thank Bill Paul (wpaul@freebsd.org) and many other people for their work
on this driver.

#
# [1] Detailed description of this bug is at:
#     FreeBSD dev/re/if_re.c rev1.70 by wpaul@freebsd.org
#
# [2] Detailed description of this bug is at:
#     FreeBSD dev/re/if_re.c rev1.71 by wpaul@freebsd.org
#