DIAMETER_Emulation: Support forwarding messages identified by ete_id to a client component

This is useful in the scenarios where the client component submits a
IMSI-based transaction such as AIR, but its answer (AIA) contains no
IMSI (as per what's specified in TS 29.272 5.2.3.1). As a result, the
received AIA message would be enqueued in the DIAMETER_UNIT.

With this new feature, the test can create an expect using the
End-to-End Identifier of the message it is going to transmit, and
receive the answer in the same DIAMETER_CLIENT port the request was
transmitted, even if it contains no IMSI.

Related: OS#5757
Change-Id: I25e44146d2c49e308c1fb490b499e70ac6045f2f
diff --git a/pgw/PGW_Tests.ttcn b/pgw/PGW_Tests.ttcn
index 7bb6910..4730040 100644
--- a/pgw/PGW_Tests.ttcn
+++ b/pgw/PGW_Tests.ttcn
@@ -72,7 +72,7 @@
 	var PDU_DIAMETER msg;
 
 	if (DIAMETER_PROC.checkstate("Connected")) {
-		f_diameter_expect(imsi);
+		f_diameter_expect_imsi(imsi);
 	}
 
 	while (true) {