vxlan: Fix L3 mode

Type: fix

Partially revert fix SEGV reported in VPP-1962
[commit a4b0541f64eef02fa0d003d8f831cfdeb45d3668]

This adds an is_l3 option to choose between L2 & L3
mode add tunnel creation time

Change-Id: Ia2c91a1099074b7d23fc031b78ed0f68628eeabe
Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>
diff --git a/src/vnet/vxlan/vxlan.h b/src/vnet/vxlan/vxlan.h
index 129bb43..be819ab 100644
--- a/src/vnet/vxlan/vxlan.h
+++ b/src/vnet/vxlan/vxlan.h
@@ -214,6 +214,7 @@
   /* we normally use is_ip4, but since this adds to the
    * structure, this seems less of a breaking change */
   u8 is_ip6;
+  u8 is_l3;
   u32 instance;
   ip46_address_t src, dst;
   u32 mcast_sw_if_index;