mac80211: fix release_reorder_timeout in scan

Even if the reorder timeout timer fires while
scanning, the frames weren't received during
scanning and therefore shouldn't be dropped.
To implement this, changes to the passive scan
RX handler simplify understanding it, because
it currently checks HW_SCANNING independently
of a packet's in-scan receive status (which
doesn't make a big difference, since scan_rx()
will only pick up probe responses and beacons,
which can't be aggregated.)

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>