mac80211: Check pending scan request after having processed mgd work

When the queued management work items are processed in
ieee80211_sta_work() an item could be removed. This could change the
anybusy from true to false, so we better check whether we can start a
new scan only after having processed the pending work first.

Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>