iwlwifi: mvm: drop UNKNOWN security type frames

In some cases we may get from FW errored frames with
UNKNOWN security type.

This may happen in unsecured aggregation flow, where
the first packet had a CRC error in the WEP bit, which
was followed by a failure to decrypt and was dropped.

The next frames in the aggregation "inherit" the bad metadata
of the first packet.

Make sure to drop such frames since RADA and other offloads
will not operate correctly which may have unexpected results.

In case of AP it also causes to TX AMSDU frames to the peers,
resulting with assert 0x104B.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>