AR5K_RX_FILTER_PROBEREQ enables reception of probe requests,
but the filter flag FIF_BCN_PRBRESP_PROMISC is actually about
receiving beacons and probe _responses_, so we shouldn't
turn on the filter when scanning.
Signed-off-by: NBob Copeland <me@bobcopeland.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>