mac80211: only remove AP VLAN frames from TXQ

When removing an AP VLAN interface, mac80211 currently purges
the entire TXQ for the AP interface. Fix this by using the FQ
API introduced in the previous patch to filter frames.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>