NAT44: do not create session record for identity mapping (VPP-1439)

Change-Id: I39a3146a4e4ba8eadf50af7113b9ae6b1c1d688f
Signed-off-by: Matus Fabian <matfabia@cisco.com>
diff --git a/test/test_nat.py b/test/test_nat.py
index 9092b47..3b9007f 100644
--- a/test/test_nat.py
+++ b/test/test_nat.py
@@ -1935,6 +1935,9 @@
             self.logger.error(ppp("Unexpected or invalid packet:", p))
             raise
 
+        sessions = self.vapi.nat44_user_session_dump(self.pg0.remote_ip4n, 0)
+        self.assertEqual(len(sessions), 0)
+
     def test_multiple_inside_interfaces(self):
         """ NAT44 multiple non-overlapping address space inside interfaces """