freebsd_wlan: Merge the new net80211 code from FreeBSD 12.

Changes to the Haiku module will come in the next commit.
There are a few Haiku-specific changes in here; most notably some
hacks to prevent struct size changes from breaking wpa_supplicant,
and a removal of the full ieee80211_channel structure from some ioctls
where we previously returned it.

freebsd11_wlan -> freebsd_wlan.

FreeBSD 12's net80211 layer contains only 2 small KPI breaks from FreeBSD 11,
so we can upgrade it, apply those 2 changes to the drivers which are affected
(as the changes are in some lesser-used functions), and then upgrade all drivers
one at a time.