MFC: if_gem.c 1.31 + 1.35, if_gem_pci.c 1.20, if_gemvar.h 1.11

• In gem_ioctl() move the call to ether_ioctl() to the default case of the switch statement in order to make this driver more like other Ethernet NIC drivers.
• In gem_attach() call gem_stop() in addition to gem_reset() to make sure the chip actually is stopped and not just reset.
• In gem_stop() also stop the gem_rint_timeout() callout in case the driver is compiled with GEM_RINT_TIMEOUT defined.
• Remove NOP spl*() calls and add locking (making gem(4) MPSAFE).

This MFC actually brings the RELENG_6 gem(4) in line with HEAD which
means that it additionally includes a comment update regarding the
IFF_OACTIVE -> IFF_DRV_OACTIVE rename which was part of if_gem.c 1.33
but missed in the respective MFC in 1.29.2.2.

Requested by: thompsa
Approved by: re (scottl)