upf: in PFCP Sess Est, use local F-TEID = CHOOSE

So far the test asked osmo-upf to use an actual IP address and TEID, but
normally it is sent with CHOOSE = 1 so that osmo-upf picks a new local
TEID and returns it with the proper local IP address in the response.

This is making the test more realistic, and also prepares for testing
Network Instance handling, where osmo-upf will need to return the proper
IP addresses for specific Network Instance names.

Change-Id: Iaba372cbb2e0cf0c5bee80b09d346f9bcb78bfbe
diff --git a/upf/UPF_Tests.ttcn b/upf/UPF_Tests.ttcn
index fb4ef08..3dd469b 100644
--- a/upf/UPF_Tests.ttcn
+++ b/upf/UPF_Tests.ttcn
@@ -633,7 +633,7 @@
 private function f_ruleset_tunend(GTP_Action gtp) return PFCP_Ruleset
 {
 	var PFCP_Ruleset rules := { {}, {} };
-	f_ruleset_add_GTP_decaps(rules, ts_PFCP_F_TEID_ipv4(gtp.teid_access_l, gtp.gtp_access_ip));
+	f_ruleset_add_GTP_decaps(rules, ts_PFCP_F_TEID_choose_v4());
 	f_ruleset_add_GTP_encaps(rules, gtp.core_ip, gtp.teid_access_r, gtp.gtp_access_ip);
 	return rules;
 }