net80211: radiotap: add more VHT flags, and struct

Add the struct for VHT information and flags for the known and flag
field as documented on radiotap.org. iwlwifi has started filling in
these details.

While here, add Copyright information for all the additions in the
last years.

Sponsored by: The FreeBSD Foundation

(cherry picked from commit 125b09de09ec5ca1939de0207090513453b5908e)