This is needed for two reasons:
* Drivers will need to know what the negotiated set of VHT capabilities
and rates are in order to configure (and reconfigure for opmode/chanwidth
changes) how to speak to a given peer; and
* Because some vendors are "special", we should be careful in what we announce
to them during peer association.
This isn't the complete solution, as I still need to make sure that when
sending out probe requests before we know what we want, we don't limit
the capabilities being announced. This is important for IBSS/mesh work
later on as probe request/response exchanges are the first hint at what
a peer supports. I'll look at adding that to the API soon.
This is a skeleton set based on ieee80211_ht.c. It implements some IE
parsing, some basic unfinished negotiation, and channel promotion/demotion.
However, by itself it's not enough to do VHT - notably, the actual
channel promotion for STA mode at least is done in ieee80211_ht.c as
part of htinfo_update_chw(). I was .. quite amused when I found that
out.
I'm checking this in so others can see progress rather than one huge
commit when VHT is "done" (which will likely be quite a while.)
