Iu: verify handling of GMM Service Request (data)when no PDP Context present.
What should the SGSN answer to GMM Service Request (type=data) when no PDP Context are active?
If there would be PDP Context, it should activate RAB Assignment Request to the RNC.
Should it ask the UE for the PDP Context Status and invalidate unknown PDP Contexts?
Should it sent GMM Service Reject?