mac80211: add AQL support for broadcast packets (#3208)

Excessive broadcast traffic with little competing unicast traffic can easily
flood hardware queues, leading to throughput issues. Additionally, filling
the hardware queues with too many packets breaks FQ for broadcast data.
Fix this by enabling AQL for broadcast packets.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: David Bauer <mail@david-bauer.net>