GGSN_Tests: Actually request the right IPv4 PCO according to the test case

Missing: Verification of returned PCO
diff --git a/ggsn_tests/GGSN_Tests.cfg b/ggsn_tests/GGSN_Tests.cfg
index 3d8bcbc..87cd456 100644
--- a/ggsn_tests/GGSN_Tests.cfg
+++ b/ggsn_tests/GGSN_Tests.cfg
@@ -14,3 +14,5 @@
 GGSN_Tests.TC_pdp6_act_deact
 GGSN_Tests.TC_pdp6_act_deact_pcodns
 GGSN_Tests.TC_pdp6_act_deact_icmp6
+
+GGSN_Tests.TC_echo_req_resp