hlr: add Check IMEI tests

Create tests for most code paths of rx_check_imei_req() in hlr.c (except
for subscriber create on demand, this will be in an upcoming patch).

Add missing message types to GSUP_Types.ttcn, and adjust the IMEI and
IMEI_Result IEs for consistency with the existing IEs, and to make the
tests compile.

Related: OS#2541
Change-Id: I97c8462f0817149feadd0c4865e3df6c2af92a80
2 files changed