ath10k: Ignore SWBA event for a vif if its marked for no beacon

Ignore processing further in SWBA event scheduled for a vif, if mac80211
has marked the particular vif for stop beaconing and brought the vdev
down in 'ath10k_control_beaconing'. This should potentially avoid ath10k
warning/error messages while running continuous wifi down/up with max
number of vaps configured. Found this change during code walk through
and going through other beacon configuration related functions in ath10k

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>