You should totally update to -HEAD to fix some ath(4) hangs

[Adrian Chadd]

Hi,

I've just committed a bunch of things to -HEAD that fix ath(4) hangs
in 11n A-MPDU transmission.

If you're doing 11n AP stuff then please update and re-test.

I'd like someone else to MFC the commits to stable/10 so people there
can benefit from it.

Thanks,

-a