CFT: Fix nframes on retried frames

[Adrian Chadd]

Hi all,

Kim has some debugging output that leads me to believe I'm not
entirely correctly clearing aggregation frame state when a buffer is
being retried.

I have a patch here which clears some of it:

http://people.freebsd.org/~adrian/ath/20120905-bfs-set-nframes.diff

I'd appreciate it if people would test this out and let me know if
they see any debugging output that has 'nframes' in it.

Once I know that this corner case is being triggered and that I've
fixed (part of) it, I'll push this into -HEAD>



Adrian