vxlan: crash on configuring vxlan tunnel on l3 mode

Configure a vxlan tunnel using this CLI and then assign an ip address to
the vxlan tunnel cause VPP to crash immediately
create vxlan tunnel src x.x.x.x dst y.y.y.y vni 1000 decap-next node ethernet-input l3
set interface ip address vxlan_tunnel0 z.z.z.z/24

It looks like when l3 mode is configured, the code calls the wrong function
to register the interface

Type: fix
Fixes: 3e38422ab905d26ab1625c74268e30c94327ea54

Signed-off-by: Steven Luong <sluong@cisco.com>
Change-Id: Ie1a08efc028f37fb528a7dfd7048ff6836bb8ddc
diff --git a/src/vnet/vxlan/vxlan.h b/src/vnet/vxlan/vxlan.h
index d6dad7a..290f03d 100644
--- a/src/vnet/vxlan/vxlan.h
+++ b/src/vnet/vxlan/vxlan.h
@@ -134,7 +134,8 @@
   u32 dev_instance;		/* Real device instance in tunnel vector */
   u32 user_instance;		/* Instance name being shown to user */
 
-    VNET_DECLARE_REWRITE;
+  VNET_DECLARE_REWRITE;
+  u8 is_l3;
 } vxlan_tunnel_t;
 
 #define foreach_vxlan_input_next        \