PCU_Tests: make sure ts_BSSGP_DL_UD includes IMSI

Whenever we send a ts_BSSGP_DL_UD via BSSGP and we expect the downlink
assignment on the paging channel by calling
f_ms_exp_dl_tbf_ass_ccch(ms), then we should make sure that
ts_BSSGP_IMSI actually contains an IMSI (paging group)

Related: OS#5927
Change-Id: I356d93edd03c7e7564bde88d34effcf1b1967621
1 file changed