urtwn: first cut of 11n

[Adrian Chadd]

hi,

here's an updated patch:

http://people.freebsd.org/~adrian/net80211/20160320-urtwn-11n-3.diff

This sets up the rate control for RTL8192CU chips.

I've tested it on RTL8188EU and RTL8192CU at this stage. I haven't
triple verified that it's transmitting 11n frames but it at least
looks like it's doing the right thing. It's certainly /receiving/
them!


-a