mwl8787: convert 802.11 AC to mac80211 AC

The 8787 firmware returns the outgoing queue priority as
an 802.11 AC, but this is different from the mac80211 AC
enumeration order. Convert this so we can dequeue /
restart the right mac80211 queues.

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>
mwl8787: set hw queue in tx descriptor

The firmware will now queue a given frame on whatever
hardware queue the user requested instead of mapping a UP.

Note the hack to keep tx aggregation working for now :(

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>