MSC_Tests: Use enum instead of magic numbers for CM_SERVICE_TYPE

Change-Id: Ic90b4a0aa47821877a2d3566606b9c9dd5919968
diff --git a/bsc/MSC_ConnectionHandler.ttcn b/bsc/MSC_ConnectionHandler.ttcn
index 39b09f6..d1be0ef 100644
--- a/bsc/MSC_ConnectionHandler.ttcn
+++ b/bsc/MSC_ConnectionHandler.ttcn
@@ -87,7 +87,7 @@
 
 function f_create_chan_and_exp(TestHdlrParams pars) runs on MSC_ConnHdlr {
 	var MobileIdentityLV mi := valueof(ts_MI_IMSI_LV(pars.imsi));
-	var PDU_ML3_MS_NW l3_info := valueof(ts_CM_SERV_REQ('0001'B, mi));
+	var PDU_ML3_MS_NW l3_info := valueof(ts_CM_SERV_REQ(CM_TYPE_MO_CALL, mi));
 	var octetstring l3_enc := enc_PDU_ML3_MS_NW(l3_info);
 
 	/* call helper function for CHAN_RQD -> IMM ASS ->EST_IND */