mac80211: move QoS-enable to BSS info

Ever since

commit e1b3ec1a
Author: Stanislaw Gruszka <sgruszka@redhat.com>
Date:   Mon Mar 29 12:18:34 2010 +0200

    mac80211: explicitly disable/enable QoS

mac80211 is telling drivers, in particular
iwlwifi, whether QoS is enabled or not.

However, this is only relevant for station mode,
since only then will any device send nullfunc
frames and need to know whether they should be
QoS frames or not. In other modes, there are
(currently) no frames the device is supposed to
send.

When you now consider virtual interfaces, it
becomes apparent that the current mechanism is
inadequate since it enables/disables QoS on a
global scale, where for nullfunc frames it has
to be on a per-interface scale.

Due to the above considerations, we can change
the way mac80211 advertises the QoS state to
drivers to only ever advertise it as "off" in
station mode, and make it a per-BSS setting.

Tested-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>