[Encrypted IMSI] Add support for EAP Method prefix

Add support for EAP method prefix in the anonymous identity
used during EAP-SIM/AKA/AKA' authentication when encrypted IMSI
is used. The prefix is a single character that indicates which
EAP method is required by the client.

Bug: 142915637
Test: Manual test
Change-Id: I0b439590ed4b73aca2b9c139a7ae4b24af1370a7
1 file changed