SGSN: print additional GTP-related info

* print libgtp version on startup
* print GSN addresses in 'sh sgsn'

Change-Id: I699a9eb56c4b362984ea8292a3d2b22b71f53c15
Related: SYS#3610
diff --git a/tests/vty_test_runner.py b/tests/vty_test_runner.py
index 104bba4..9b8c560 100644
--- a/tests/vty_test_runner.py
+++ b/tests/vty_test_runner.py
@@ -152,7 +152,7 @@
         self.assertTrue(self.vty.verify('show bssgp stats', ['']))
         self.assertTrue(self.vty.verify('show bssgp nsei 123', ['']))
         self.assertTrue(self.vty.verify('show bssgp nsei 123 stats', ['']))
-        self.assertTrue(self.vty.verify('show sgsn', ['']))
+        self.assertTrue(self.vty.verify('show sgsn', ['  GSN: signalling 127.0.0.1, user traffic 127.0.0.1']))
         self.assertTrue(self.vty.verify('show mm-context all', ['']))
         self.assertTrue(self.vty.verify('show mm-context imsi 000001234567', ['No MM context for IMSI 000001234567']))
         self.assertTrue(self.vty.verify('show pdp-context all', ['']))