Add a separate bit in struct ieee80211_tx_info to indicate airtime tracked
as broadcast/multicast. This avoids a race condition where airtime from
stations that were just removed wasn't getting subtracted from the total
PHY airtime.
Fixes: 95e633efbd1b ("mac80211: add AQL support for broadcast/multicast packets")
Signed-off-by: Felix Fietkau <nbd@nbd.name>