In a situation where:
	- The remote host sends a FIN
	- in an ACK for a sequence number for which an ACK has already
	  been received
	- There is still unacked data on route to the remote host
	- The packet does not contain a window update

The packet may be dropped without processing the FIN flag.

PR:		kern/99188
Submitted by:	Staffan Ulfberg <staffan@ulfberg.se>
Discussed with:	andre
MFC after:	never
Partial revert of r258779 and r258780:
	The directory sys/dev/drm2/i915 is apperently contributed code.
	Revert to the broken version of this file to make future imports easier.

Requested by:	kib
Add some code to double-check whether we're correctly populating the
TX ring according to what the firmware requires.

The firmware requires A-MPDU sub-frames to be at a very specific ring
offset - that is, the ring slot offset should be (seqno % 256.)

This holds for every NIC I've tested thus far except the 4965,
which starts erroring out here shortly before the firmware panics.
Which is good, it's doing what it's supposed to (read: capture that
we've screwed up somewhere.)

The specifics about getting this stuff right:

* the initial seqno allocation should match up with the ringid.
* .. yes, this means we can start at a ring offset that isn't zero.
* .. because we program the start seqno in the firmware message
  to setup the AC.
* The initial seqno allocation may be non-zero _and_ frames may be
  being transmitted during a-mpdu negotiation.  I faced similar
  issues on ath(4) and had to software queue frames to that node+TID
  during A-MPDU negotiation.
* seqno allocation should be in lockstep with ring increments.
* If we fail to transmit some segment, no, we shouldn't reuse that
  ring slot.  We should just transmit a BAR (which we aren't yet
  doing, sigh) and move onto the next seqno.
* In theory there shouldn't be any holes in the seqno space when
  we are transmitting frames.

Tested:

* 4965 (throws problems, so yes we have to fix this);
* 5100 (seems ok);
* 6200 (seems ok);
* 2200 (seems ok);
* 2230 (seems ok).
Add some sanity checks to the TLV fetch.

Obtained from:	Linux iwlwifi
Oops - fix bad indent. Sorry!