Track and expose the latest statistics from the firmware.

Tested:

* Intel Centrino 6205
Add a very basic and totally hacked up iwnstats program.

This just extracts the current statistics out from the NIC via
the new ioctl API and displays them.  It runs every 100ms to hopefully
grab the latest statistics.

I may eventually teach this to use libstatfoo like what has been done
for athstats and such; but this is good enough for now for people to
do some basic investigation.

Tested:

* Intel Centrino 6205