Add interface to disable/enable QoS (aka WMM or WME). Currently drivers
enable it explicitly when ->conf_tx method is called, and newer disable.
Disabling is needed for some APs, which do not support QoS, such
we should send QoS frames to them.
Signed-off-by: NStanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>