SNAT: add static mappings with unresolved external interface address to snat_static_mapping_dump

Change-Id: Ib560b397700fe058ad1e2970989d98e3debf54aa
Signed-off-by: Matus Fabian <matfabia@cisco.com>
diff --git a/test/test_snat.py b/test/test_snat.py
index 967d4b3..9d2070a 100644
--- a/test/test_snat.py
+++ b/test/test_snat.py
@@ -790,9 +790,11 @@
         self.snat_add_static_mapping('1.2.3.4',
                                      external_sw_if_index=self.pg7.sw_if_index)
 
-        # no static mappings
+        # static mappings with external interface
         static_mappings = self.vapi.snat_static_mapping_dump()
-        self.assertEqual(0, len(static_mappings))
+        self.assertEqual(1, len(static_mappings))
+        self.assertEqual(self.pg7.sw_if_index,
+                         static_mappings[0].external_sw_if_index)
 
         # configure interface address and check static mappings
         self.pg7.config_ip4()
@@ -800,6 +802,7 @@
         self.assertEqual(1, len(static_mappings))
         self.assertEqual(static_mappings[0].external_ip_address[0:4],
                          self.pg7.local_ip4n)
+        self.assertEqual(0xFFFFFFFF, static_mappings[0].external_sw_if_index)
 
         # remove interface address and check static mappings
         self.pg7.unconfig_ip4()