mac80211: decouple # of netdev queues from HW queues

When we get more hardware queues, we'll still want
to only have netdev queues per AC, so set it up in
that way. If the hardware doesn't support QoS (by
not supporting at least 4 queues) the netdevs get
a single queue only (this is no change in behavior
as there are no drivers with 2 or 3 queues today.)

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