ath9k: use separate HW queue for each channel context

Use seperate tx queue for each AC in each channel context and expose
these information to mac80211 to avoid stopping one channel context
leads to stopping the entire traffic for that AC even on other contexts.

Signed-off-by: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>