mac80211: Restart STA timers only on associated state

A panic was observed when the device is failed to resume properly,
and there are no running interfaces. ieee80211_reconfig tries
to restart STA timers on unassociated state.

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