EAP-SIM/AKA: Add support for anonymous@realm

EAP-SIM/AKA: Add support for anonymous@realm

SIM-based EAP authentication with IMSI encryption requires a special EAP
Identity response: anonymous@realm. Then the server sends AKA-Identity
request which is answered with the encrypted IMSI. Add logic that
indicates if the special anonymous identity is used. Otherwise, this
field is used for storing the pseudonym.

Test: Connect to Carrier Wi-Fi, verify correct behavior from captures
Test: Connect to non IMSI encrypted EAP-AKA AP, verify pseudonym usage
Signed-off-by: Hai Shalom <haishalom@google.com>