GRE tunnel key includes the FIB table

- GRE tunnels with the same src,dst addresses are not the same tunnel
- Two data-plane improvements:
  - the cached key was never updated and so useless
  - no need to dereference the tunnel's HW interface to get the sw_if_index

Change-Id: I2f2ea6e08c759a810b753cec22c497e921a2ca01
Signed-off-by: Neale Ranns <nranns@cisco.com>

test/test_gre.py

@@ -673,6 +673,25 @@ class TestGRE(VppTestCase):
         rx = self.pg0.get_capture(len(tx))
         self.verify_decapped_4o4(self.pg0, rx, tx)
 
+        #
+        # Send tunneled packets that match the created tunnel and
+        # but arrive on an interface that is not in the tunnel's
+        # encap VRF, these are dropped
+        #
+        self.vapi.cli("clear trace")
+        tx = self.create_tunnel_stream_4o4(self.pg2,
+                                           "2.2.2.2",
+                                           self.pg1.local_ip4,
+                                           self.pg0.local_ip4,
+                                           self.pg0.remote_ip4)
+        self.pg1.add_stream(tx)
+
+        self.pg_enable_capture(self.pg_interfaces)
+        self.pg_start()
+
+        self.pg0.assert_nothing_captured(
+            remark="GRE decap packets in wrong VRF")
+
         #
         # test case cleanup
         #