11n in adhoc mode

[Adrian Chadd]

Here's what I have trimmed this down to so far:

http://people.freebsd.org/~adrian/ath/20121212-11n-ibss-and-other-stuff-3.diff

Please disable ampdu for now (ifconfig wlanX -ampdu) as it just plain
doesn't work.
I'll figure out why once I figure out the cleanest way to get this 11n
IBSS stuff working.

I've tested this between two 11n nodes and a third 11a only node.
So far it works out ok. But it obviously could do with a lot more
thorough testing.

I'd appreciate feedback!



Adrian