mac80211: Support BIGTK configuration for Beacon protection

Extend mac80211 key configuration to support the new BIGTK with key
index values 6 and 7. Support for actually protecting Beacon frames
(adding the MME in AP mode and checking it in STA mode) is covered in
separate commits.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
Link: https://lore.kernel.org/r/20200222132548.20835-3-jouni@codeaurora.org


Signed-off-by: Johannes Berg <johannes.berg@intel.com>