- 6-CURRENT's seems to have started pushing 802.11 events through the routing
  socket. check if making LowLevel.read_routemsg propagate these up would be
  useful.

- I think ARP entry additions and expiries also come through the routing
  socket. check, and decide whether to do something with it.

- integrate MAC.ml and Iface.ml. They deal in mostly the same issues, ethernet
  interfaces and their addresses.