Pull up following revision(s) (requested by msaitoh in ticket #1910):

sys/dev/pci/if_wm.c: revision 1.785
sys/dev/pci/if_wm.c: revision 1.786
sys/dev/pci/if_wm.c: revision 1.787
sys/dev/pci/if_wm.c: revision 1.788
sys/dev/pci/if_wm.c: revision 1.789

wm(4): Use SCVPC and HRMPC for 82575 and newer.
  The SCVPC(SerDes/SGMII Code Violation Packet Count) register and the HRMPC
  (Header Redirection Missed Packet Count) register were added in if_wm.c
  rev. 1.776 but the location in the code were incorrect. Fix them.

wm(4): Add some info to some event counters.
- The difference between the RUC(Rx Undersize) and RFC(Rx Fragment) is whether
  the CRC is valid or not.
- The difference between the ROC(Rx Oversize) and RJC(Rx Jabber) is whether
  the CRC is valid or not.
- LENERRS(Length Errors) is for the length/type field <= 1500.

wm(4): the IAC(Interrupt Assertion Count) register is for 82571 and newer.

wm(4): Modify descriptions of flow control related event counters.

wm(4): Replace /* nothing */ to __nothing for evcnt macros
Prevent empty if bodies for !WM_EVENT_COUNTERS.

(martin)