WPA: Ignore unauthenticated encrypted EAPOL-Key data

Ignore unauthenticated encrypted EAPOL-Key data in supplicant
processing. When using WPA2, these are frames that have the Encrypted
flag set, but not the MIC flag.

When using WPA2, EAPOL-Key frames that had the Encrypted flag set but
not the MIC flag, had their data field decrypted without first verifying
the MIC. In case the data field was encrypted using RC4 (i.e., when
negotiating TKIP as the pairwise cipher), this meant that
unauthenticated but decrypted data would then be processed. An adversary
could abuse this as a decryption oracle to recover sensitive information
in the data field of EAPOL-Key messages (e.g., the group key).
(CVE-2018-14526)

Signed-off-by: Mathy Vanhoef <Mathy.Vanhoef@cs.kuleuven.be>

Obtained from: git://w1.fi/hostap.git
MFC after: 1 day
Security: CVE-2018-14526
Security: VuXML: 6bedc863-9fbe-11e8-945f-206a8a720317