Fix antenna configuration, microcode version checks and rate selection
in preparation for the 5300 3x3 NIC.

During this particular adventure, I did indeed discover that a whole
swath of things made little to no sense.

Those included, and are fixed here:

* A lot of the antenna configuration bits assume the NIC has two receive
  chains.  That's blatantly untrue for NICs that don't.
* There was some disconnect between the antenna configuration when
  forming a PLCP rate DWORD (which includes the transmit antenna
  configuration), separate to the link quality antenna configuration.

  So now there's helper functions to return which antenna configurations
  to use and those are used wherever an antenna config is required.

* The 5300 does up to three stream TX/RX (so MCS0->23), however
  the link quality table has only 16 slots.  This means all of the
  rate entries are .. well, dual-stream rates.  If this is the case,
  the "last MIMO" parameter can't be 16 or it panics the firmware.
  Set it to 15.

* .. and since yes it has 16 slots, it only would try retransmitting
  from MCS8->MCS23, which can be quite .. terrible.  Hard-code the last
  two retry slots to be the lowest configured rate.

* I noticed some transmit configuration command stuff is different
  based on firmware API version, so I lifted that code from Linux.

* Add / augment some more logging to make it easier to capture this
  stuff.

Now, 3x3 is still terrible because the link quality configuration is
plainly not good enough.  I'll have to think about that.
However, the original goal of this - 3x3 operation on the Intel
5300 NIC - actually worked.

There are also rate control bugs in the way this driver handles
notifying the net80211 rate control code when AMPDU is enabled.
It always steps the rate up to the maximum rate possible - and
this eventually ends in much sadness.  I'll fix that later.

As a side note - 2GHz HT40 now works on all the NICs I have tested.

As a second side note - this exposed some bad 3x3 behaviour in
the ath(4) rate control code where it starts off at a 3-stream rate
and doesn't downgrade quickly enough.  This makes the initial
dhcp exchange take a long time.  I'll fix the ath(4) rate code
to start at a low fixed 1x1 MCS rate and step up if everything
works out.

Tested:

* Intel 2200
* Intel 2230
* Intel 5300
* Intel 5100
* Intel 6205
* Intel 100

TODO:

* Test the other NICs more thoroughly!

Thank you to Michael Kosarev <russiane39@gmail.com> for donating the
Intel 5300 NIC and pestering me about it since last year to try and
make it all work.