ggsn: Verify presence of DNS addresses in IPCP of PCO

If we request DNS in IPCP in PCO, we also expect a corresponding result.
diff --git a/ggsn_tests/gen_links.sh b/ggsn_tests/gen_links.sh
index ee8d7b0..6dd2d62 100755
--- a/ggsn_tests/gen_links.sh
+++ b/ggsn_tests/gen_links.sh
@@ -44,5 +44,5 @@
 gen_links $DIR $FILES
 
 DIR=../library
-FILES="General_Types.ttcn GSM_Types.ttcn Osmocom_Types.ttcn Native_Functions.ttcn Native_FunctionDefs.cc"
+FILES="General_Types.ttcn GSM_Types.ttcn Osmocom_Types.ttcn Native_Functions.ttcn Native_FunctionDefs.cc IPCP_Types.ttcn"
 gen_links $DIR $FILES