HLR: Add HLR_EUSE.ttcn to implement minimal external USSD Entity

As OsmoHLR is getting support for external USSD Entities (EUSEs),
we have to implement this function in the test logic in order to
test it.

Change-Id: Ibab210b06abfd5a21e81c7f7fbe574c4f67414a0
diff --git a/library/GSUP_Types.ttcn b/library/GSUP_Types.ttcn
index 6044565..ba8180f 100644
--- a/library/GSUP_Types.ttcn
+++ b/library/GSUP_Types.ttcn
@@ -687,4 +687,15 @@
 	}
 );
 
+function f_gsup_find_ie(GSUP_PDU msg, GSUP_IEI iei, out GSUP_IeValue ret) return boolean {
+	for (var integer i := 0; i < sizeof(msg.ies); i := i+1) {
+		if (msg.ies[i].tag == iei) {
+			ret := msg.ies[i].val;
+			return true;
+		}
+	}
+		return false;
+}
+
+
 } with { encode "RAW"; variant "FIELDORDER(msb)" }