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
diff --git a/pcu/PCU_Tests.ttcn b/pcu/PCU_Tests.ttcn
index ba27e58..012a0be 100644
--- a/pcu/PCU_Tests.ttcn
+++ b/pcu/PCU_Tests.ttcn
@@ -479,7 +479,7 @@
 
 	/* New data arrives, PCU should page the MS since no TBF active exists: */
 	/* Send some more data, it will never reach the MS */
-	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data));
+	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data, imsi := ts_BSSGP_IMSI(ms.imsi)));
 	f_ms_exp_dl_tbf_ass_ccch(ms);
 
 	f_shutdown(__BFILE__, __LINE__, final := true);
@@ -1785,7 +1785,7 @@
 	f_sleep(int2float(info_ind.t3191));
 
 	/* The TBF should be freed now, so new data should trigger an Assignment: */
-	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data2));
+	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data2, imsi := ts_BSSGP_IMSI(ms.imsi)));
 	f_ms_exp_dl_tbf_ass_ccch(ms);
 
 	/* Wait timer X2002 and DL block is available after CCCH IMM ASS: */
@@ -1860,7 +1860,7 @@
 	f_sleep(int2float(info_ind.t3191));
 
 	/* The TBF should be freed now, so new data should trigger an Assignment: */
-	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data2));
+	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data2, imsi := ts_BSSGP_IMSI(ms.imsi)));
 	f_ms_exp_dl_tbf_ass_ccch(ms);
 
 	/* Wait timer X2002 and DL block is available after CCCH IMM ASS: */
@@ -3128,10 +3128,10 @@
 	for (var integer i := 0; i < 10; i := i + 1) {
 		BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data_sapi_other, imsi := ts_BSSGP_IMSI(ms.imsi)));
 	}
-	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data_sapi2));
-	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data_sapi7));
-	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data_sapi8));
-	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data_sapi1));
+	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data_sapi2, imsi := ts_BSSGP_IMSI(ms.imsi)));
+	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data_sapi7, imsi := ts_BSSGP_IMSI(ms.imsi)));
+	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data_sapi8, imsi := ts_BSSGP_IMSI(ms.imsi)));
+	BSSGP[0].send(ts_BSSGP_DL_UD(ms.tlli, data_sapi1, imsi := ts_BSSGP_IMSI(ms.imsi)));
 	f_ms_exp_dl_tbf_ass_ccch(ms);
 
 	/* Wait timer X2002 and DL block is available after CCCH IMM ASS */