Changes

SGSN: BSSGP_ConnHdlr: GMM Service Request: handle PMM IDLE UE correct

24.008: 4.7.13.3: explicit mention the completion of the low layer security to be an implicit
Security Command Accept if the UE is in PMM Idle.
Extend the as_service_request() to handle both cases when UE is in PMM-IDLE as well in
PMM-CONNECTED.

Change-Id: I29237997e414aea80f254247da54f909410a4b36