mac80211: AMPDU handling for Extended Key ID

IEEE 802.11 - 2016 forbids mixing MPDUs with different keyIDs in one
A-MPDU. Drivers supporting A-MPDUs and Extended Key ID must actively
enforce that requirement due to the available two unicast keyIDs.

Allow driver to signal mac80211 that they will not check the keyID in
MPDUs when aggregating them and that they expect mac80211 to stop Tx
aggregation when rekeying a connection using Extended Key ID.

Signed-off-by: Alexander Wetzel <alexander@wetzel-home.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>