GRE tests and fixes

Change-Id: I234240e9bdd4b69ad64a17b1449ae1e81c0edaca
Signed-off-by: Neale Ranns <nranns@cisco.com>
diff --git a/test/vpp_sub_interface.py b/test/vpp_sub_interface.py
index b387d27..027a24b 100644
--- a/test/vpp_sub_interface.py
+++ b/test/vpp_sub_interface.py
@@ -41,6 +41,9 @@
     def add_dot1_layer(self, pkt):
         pass
 
+    def remove_vpp_config(self):
+        self.test.vapi.delete_subif(self._sw_if_index)
+
 
 class VppDot1QSubint(VppSubInterface):