MFC r272730,273018:
  Add support for QAC AR816x/AR817x Gigabit/Fast Ethernet controllers.
  These controllers seem to have the same feature of AR813x/AR815x and
  improved RSS support(4 TX queues and 8 RX queues).  alc(4) supports
  all hardware features except RSS.  I didn't implement RX checksum
  offloading for AR816x/AR817x just because I couldn't get
  confirmation from the Vendor whether AR816x/AR817x corrected its
  predecessor's RX checksum offloading bug on fragmented packets.
  This change adds supports for the following controllers.
   o AR8161 PCIe Gigabit Ethernet controller
   o AR8162 PCIe Fast Ethernet controller
   o AR8171 PCIe Gigabit Ethernet controller
   o AR8172 PCIe Fast Ethernet controller
   o Killer E2200 Gigabit Ethernet controller
MFC r272731:
  Document newly added controller AR816x/AR817x.