MSC_Tests: add testcase TC_sgsap_impl_imsi_det_eps

We have a testcase that sends an explicit (UE-Initiated) imsi detach
from EPS services. Lets also cover the case for an implicit
(Network-initated) detach.

Change-Id: I63ebc32ae457dd74214d4abee4f511cde28de4a7
Related: OS#3614
2 files changed