ggsn_tests: Configure expected GGSN DNS values and improve error message

Change-Id: Ie64ca0b4cda22fd358c8c304d5b3909fd9685948
diff --git a/ggsn_tests/GGSN_Tests.cfg b/ggsn_tests/GGSN_Tests.cfg
index e97578c..90368b9 100644
--- a/ggsn_tests/GGSN_Tests.cfg
+++ b/ggsn_tests/GGSN_Tests.cfg
@@ -14,8 +14,10 @@
 [MODULE_PARAMETERS]
 GGSN_Tests.m_bind_ip_gtpc := "127.0.42.1"
 GGSN_Tests.m_bind_ip_gtpu := "127.0.42.1"
-GGSN_Tests.m_ggsn_ip_gtpc := "127.0.23.1"
-GGSN_Tests.m_ggsn_ip_gtpu := "127.0.23.1"
+GGSN_Tests.m_ggsn_ip_gtpc := "127.0.0.2"
+GGSN_Tests.m_ggsn_ip_gtpu := "127.0.0.2"
+GGSN_Tests.m_ggsn_ip4_dns1 := "192.168.100.1"
+GGSN_Tests.m_ggsn_ip4_dns2 := "8.8.8.8"
 
 [EXECUTE]
 #GGSN_Tests.TC_dummy