net80211: prevent plaintext injection by A-MSDU RFC1042/EAPOL frames
No longer accept plaintext A-MSDU frames that start with an RFC1042
header with EtherType EAPOL. This is done by only accepting EAPOL
packets that are included in non-aggregated 802.11 frames.
Note that before this patch, FreeBSD also only accepted EAPOL frames
that are sent in a non-aggregated 802.11 frame due to bugs in
processing EAPOL packets inside A-MSDUs. In other words,
compatibility with legitimate devices remains the same.
This relates to section 6.5 in the 2021 Usenix "FragAttacks" (Fragment
and Forge: Breaking Wi-Fi Through Frame Aggregation and Fragmentation)