work around an athn(4) device problem with bogus Michael MIC failures
Clients using Tx aggregation against an athn(4) hostap will send block ack
request control frames whenever they need to sync their Tx block ack window.
athn(4) dropped such frames due to bogus Michael MIC failures reported by
the hardware decryption engine. Ignore such failures for control frames in
order to fix athn(4) hostap mode against clients which use Tx aggregation.
Additionally, only report Michael MIC failures to the net80211 stack if the
offending client is actually using TKIP, which would also have prevented the
problem since we require CCMP as group cipher in our default configuration.
Problem reported and fix tested by kettenis@