Extend mechanism to distinguish EAPOL-Key msg 2/4 from 4/4

Extend mechanism to distinguish EAPOL-Key msg 2/4 from 4/4

The initial Authenticator implementation depended on the Key Data field
being empty for EAPOL-Key msg 4/4. This worked fine for years in
practice, but in theory, vendor specific elements or KDEs could have
been added inti EAPOL-Key msg 4/4 and that would have broken this
design. In addition, the MLD case did introduce a KDE into EAPOL-Key msg
4/4 and required changes here.

As an initial step to make this more robust for future extensions,
recognize a received EAPOL-Key message as msg 4/4 if it is for RSN
(i.e., not WPAv1), has Secure=1, contains an unencrypted Key Data field,
and does not include RSNE.

Signed-off-by: Jouni Malinen <quic_jouni@quicinc.com>