ath9k: BT coex performance tuning for AR9462

Use smaller aggregation limit and increasing aggregation threshold
for osla that could improve wlan performance when there is HID profile.

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