Changes

SGSN: BSSGP_ConnHdlr: GMM Service Request: optional expect an authentication

On a Service Request, the authentication is optional.
Either an authentication can happen or the key material from the previous authentication
has to be used. Extend the test case to allow both cases
to succeed.

Change-Id: I9ed08160bf5413e3a30d6e90eb947d4d799e1058