iwlwifi: mvm: fix beacon protection checks

Unfortunately, since beacon protection isn't fully available
yet, we didn't notice that there are problems with it and
that the replay detection isn't working correctly. We were
relying only on mac80211, since iwl_mvm_rx_crypto() exits
when !ieee80211_has_protected(), which is of course true for
protected (but not encrypted) management frames.

Fix this to properly detect protected (but not encrypted)
management frames and handle them - we continue to only care
about beacons since for others everything can and will be
checked in mac80211.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Fixes: b1fdc250

 ("iwlwifi: mvm: advertise BIGTK client support if available")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20210326125611.23c990843369.I09c262a8f6f9852cc8f513cdcb31a7f8f87dd8af@changeid