mac80211: enable QoS explicitly in AP mode

Enable QoS explicitly, when user space AP program will setup a QoS
queues. Currently this is not needed as iwlwifi not work in AP mode
and no other driver implement enable/disable QoS.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>