net80211: adjust more VHT structures/fields

Replace ieee80211_ie_vhtcap with ieee80211_vht_cap and
ieee80211_ie_vht_operation with ieee80211_vht_operation.
The "ie" version has the two bytes type/length at the beginning which
we did not actually use as such (the one place doing did just as unused
extra work).

Using the non-"ie" versions allows us to re-use them on shared code.
Using an enum helps us to not accidentally get unsuppored or unhandled
values tough we cannot use it in the struct as we need to ensure the
field width.

ieee80211_vht_operation is guarded by _KERNEL/WANT_NET80211. While the
header is supposed to be exported to user land historically, software
such as wpa bring their own structure definitions. For in-tree usage
it is only ifconfig which really cares (at least for now).

Sponsored by: The FreeBSD Foundation
MFC after: 3 days
Reviewed by: adrian (earlier), cc
Differential Revision: https://reviews.freebsd.org/D42901

net80211: add ieee80211_add_vhtcap_ch()

Add an implementation of ieee80211_add_vhtcap() which works based on
information derived from the vap (and possibly channel/band but we do
not support that yet in net80211). This is needed for scans request
information in LinuxKPI at times before we have a BSS.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days
Reviewed by: adrian, cc
Differential Revision: https://reviews.freebsd.org/D42422

sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

[net80211] Commit files missing in the previous commit

These belong to my previous commit, but apparently I typed ieee80211_vhf.[ch]
and forgot ht.h. Le oops.

[net80211] create a helper function to calculate the station facing VHT capabilities.

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.

[net80211] Add initial VHT support routines.

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.)