smpp_test_runner.py: fix socket leak

Each running test would open up another socket without ever closing unused
ones. Close the sockets after each test is done.

Change-Id: I0a42caab3bb8c9c9d04b033e4de9efe0ca8fd2af

openbsc/tests/smpp_test_runner.py

@@ -54,6 +54,8 @@ class TestVTYBase(unittest.TestCase):
         self.vty = obscvty.VTYInteract(appstring, "127.0.0.1", appport)
 
     def tearDown(self):
+        if self.vty:
+            self.vty._close_socket()
         self.vty = None
         osmoutil.end_proc(self.proc)