MSC_Tests: Use enum instead of magic numbers for CM_SERVICE_TYPE

Change-Id: Ic90b4a0aa47821877a2d3566606b9c9dd5919968
diff --git a/msc_tests/BSC_ConnectionHandler.ttcn b/msc_tests/BSC_ConnectionHandler.ttcn
index 25f8daf..330f25a 100644
--- a/msc_tests/BSC_ConnectionHandler.ttcn
+++ b/msc_tests/BSC_ConnectionHandler.ttcn
@@ -101,7 +101,7 @@
 /* helper function to fully establish a dedicated channel */
 function f_establish_fully(MobileIdentityLV mi, boolean expect_auth)
 runs on BSC_ConnHdlr {
-	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 PDU_DTAP_MT dtap_mt;
 
 	/* Send BSSAP_Conn_Req with COMPL L3 INFO to MSC */