mac80211: Do not queue Probe Request frames for station MLME

Cooked monitor interfaces cannot currently receive Probe Request
frames when the interface is in station mode. However, we do not
process Probe Request frames internally in the station MLME, so there
is no point in queueing the frame here. Remove Probe Request frames
from the queued frame list to allow cooked monitor interfaces to
receive these frames.

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