Bring over the QoS logic from the Linux r92su driver.

• the tx descriptor TID is priority, not TID.
• the tx descriptor queue id mapping is separate from the TID/priority; rather than just "BE".

TODO:

• go and re-re-re-verify the queue mappings; the linux and openbsd mappings aren't exactly the same. I need to verify all of this before I try to flip on 11n RX.