net80211: add more 802.11ac Element IDs

Add more Element IDs for VHT (11ac) to complete the current list
and we can use them if/as needed.

Sposnored by: The FreeBSD Foundation
Reviewed by: adrian
Differential Revision: https://reviews.freebsd.org/D35977

(cherry picked from commit a78be09e4d1aa8a2117f71d96093d4884c211903)