mac80211: move "bufferable MMPDU" check to fix AP mode scan

The check needs to apply to both multicast and unicast packets,
otherwise probe requests on AP mode scans are sent through the multicast
buffer queue, which adds long delays (often longer than the scanning
interval).

Cc: stable@vger.kernel.org
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>