Add "show gsup-connections" VTY command

This can help with debugging and give operational insight.

Change-Id: I977b4b8cdb36dab42b3d736a28d8b5f17cff04cd
diff --git a/tests/test_nodes.vty b/tests/test_nodes.vty
index 5afa144..21809c8 100644
--- a/tests/test_nodes.vty
+++ b/tests/test_nodes.vty
@@ -16,6 +16,7 @@
   show talloc-context (application|all) (full|brief|DEPTH)
   show talloc-context (application|all) (full|brief|DEPTH) tree ADDRESS
   show talloc-context (application|all) (full|brief|DEPTH) filter REGEXP
+  show gsup-connections
   subscriber (imsi|msisdn|id) IDENT show
 
 OsmoHLR> enable