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

commit 277d916fc2e959c3f106904116bb4f7b1148d47a upstream.

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).

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>