[net80211] address seqno allocation for group addressed frames

After some digging and looking at packet traces, it looks like the
sequence number allocation being done by net80211 doesn't meet
802.11-2012.

Specifically, group addressed frames (broadcast, multicast) have
sequence numbers allocated from a separate pool, even if they're
QoS frames.

This patch starts to try and address this, both on transmit and
receive.

• When receiving, don't throw away multicast frames for now. It's sub-optimal, but until we correctly track group addressed frames via another TID counter, this is the best we can do.

• When doing A-MPDU checks, don't include group addressed frames in the sequence number checks.

• When transmitting, don't allocate group frame sequence numbers from the TID, instead use the NONQOS TID for allocation.

This may fix iwn(4) 11n because I /think/ this was one of the
handful of places where ni_txseqs[] was being assigned /outside/
of the driver itself.

This however doesn't completely fix things - notably the way that
TID assignment versus WME assignment for driver hardware queues
will mess up multicast ordering. For example, if all multicast
QoS frames come from one sequence number space but they're
expected to obey the QoS value assigned, they'll end up in
different queues in the hardware and go out in different
orders.

I can't fix that right now and indeed fixing it will require some
pretty heavy lifting of both the WME<->TID QoS assignment, as well
as figuring out what the correct way for drivers to behave.

For example, both iwn(4) and ath(4) shouldn't put QoS multicast
traffic into the same output queue as aggregate traffic, because
the sequence numbers are all wrong. So perhaps the correct thing
to do there is ignore the WME/TID for QoS traffic and map it all
to the best effort queue or something, and ensure it doesn't
muck up the TID/blockack window tracking. However, I'm /pretty/
sure that is still going to happen.

.. maybe I should disable multicast QoS frames in general as well,
but I don't know what that'll do for whatever the current state
of 802.11s mesh support is.

Tested:

• STA mode, ath10k NIC
• AP mode, AR9344/AR9580 AP
• iperf tcp/udp tests with concurrent multicast QoS traffic.

Before this, iperfs would fail pretty quickly because the sending
AP would start sending out QoS multicast frames that would be
out of order from the rest of the TID traffic, causing the blockack
window to get way, way out of sync.

This now doesn't occur.

TODO:

• verify which QoS frames SHOULD be tagged as M_AMPDU_MPDU. For example, QoS NULL frames shouldn't be tagged!

Reviewed by: avos
Differential Revision: https://reviews.freebsd.org/D9357