SIP_Emulation: Match empty port as default port 5060

Change-Id: I8415571a5bdc99e8cc007bb4b57bcb73b7afd4fb
diff --git a/library/SIP_Emulation.ttcn b/library/SIP_Emulation.ttcn
index 5c00c4d..4aef536 100644
--- a/library/SIP_Emulation.ttcn
+++ b/library/SIP_Emulation.ttcn
@@ -380,6 +380,9 @@
 		}
 		if (not ispresent(t_exp.hostPort.portField)) {
 			t_exp.hostPort.portField := *;
+		} else if (valueof(t_exp.hostPort.portField) == 5060) {
+			/* if the port number is 5060, it may be omitted */
+			t_exp.hostPort.portField := 5060 ifpresent;
 		}
 		if (not ispresent(t_exp.urlParameters)) {
 			t_exp.urlParameters := *;