b43: Really disable QoS, if requested

Currently, when QoS-disable is requested, we would leave QoS enabled
in firmware, but only queue frames on one queue.
Change that and also tell firmware about disabled QoS, so it
completely ignores all the QoS parameters. Also don't upload the parameters,
if QoS is disabled.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>