NAT: VPP-1646 test case asserts

Change-Id: I466cea5cbe82a34d4b0b20a76bf5df4d529670e4
Signed-off-by: Filip Varga <fivarga@cisco.com>
diff --git a/test/test_nat.py b/test/test_nat.py
index e0e50c0..cbc48d4 100644
--- a/test/test_nat.py
+++ b/test/test_nat.py
@@ -3990,6 +3990,7 @@
             self.verify_capture_in(capture, self.pg0)
 
         finally:
+            self.nat44_add_address(self.nat_addr, is_add=0)
             self.pg1.unconfig_ip4()
             self.pg2.unconfig_ip4()
             self.pg1.set_table_ip4(0)