ath9k: skip beaconing when reset work is pending

Whenever the reset work is queued up, do not generate beacon. And also
clear the beacon miss count once the beacon stuck was observed.

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