stp: Ignore M3UA SSNM messages in tests

The tests were written without considering the arrival of such messages;
however, it is well within the M3UA spec that such messages appear at
any time indicating remote point code availability etc.

In libosmo-sccp.git Id92be4691b0fd77598a6edb642c028bbd8c5b623 we start
generating those messages in osmo-stp.

Let's ignore them in the tests to avoid unexpected failures.

Later on, we likely will introduce / adapt tests to actually expect
those messages whenever appropriate.

Change-Id: I85ce8fd4f26db184833cf348293f0255bb5eaac3
Related: OS#2623
diff --git a/stp/STP_Tests_M3UA.ttcn b/stp/STP_Tests_M3UA.ttcn
index 22272f3..b76d9be 100644
--- a/stp/STP_Tests_M3UA.ttcn
+++ b/stp/STP_Tests_M3UA.ttcn
@@ -75,6 +75,14 @@
 	[] any from M3UA.receive(tr_SctpPeerAddrChange) { repeat; }
 }
 
+private altstep as_m3ua_ssnm_ignore() runs on RAW_M3UA_CT {
+	var M3UA_RecvFrom rx;
+	[] any from M3UA.receive(t_M3UA_RecvFrom(tr_M3UA_SSNM)) -> value rx {
+		log("Ignoring M3UA SSNM", rx);
+		repeat;
+		}
+}
+
 friend function f_M3UA_send(integer idx, template (present) PDU_M3UA msg, template integer stream := 0)
 runs on RAW_M3UA_CT {
 	M3UA[idx].send(t_M3UA_Send(g_m3ua_conn_id[idx], msg, stream));
@@ -183,6 +191,7 @@
 	f_init_common();
 
 	activate(as_m3ua_sctp());
+	activate(as_m3ua_ssnm_ignore());
 
 	for (i := 0; i < NR_M3UA; i:=i+1) {
 		map(self:M3UA[i], system:M3UA_CODEC_PT);