luci-mod-admin-full: add support for 802.11w options

Add support for IEEE802.11w Management Frame Protection options.

Mention in the help text that the full version of wpad/hostapd is
needed.

Currently supported by ath9k and ath10k, and in LEDE also by
mwlwifi and mt76.

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>