ath9k_htc: Fix AMPDU subframe handling

* Register the driver's maximum ampdu subframe limit to mac80211.
* Cleanup the target capabilities structure and fix an endian issue.
* Fix BTCOEX by sending a command to the target when the BT priority
  changes.
* Bump the required firmware version to 1.1

Signed-off-by: Sujith Manoharan <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>