nat: fix forwarding handoff workaround

A special case when out2in packet needs to
be handoffed to other worker thread. We are
not able to determine which thread they belong
to in the first processing of nat handoff node.
These packets needs to go through out2in slowpath
before we are able to tell where to handoff them.

Type: fix
Ticket: VPP-1941

Change-Id: I7173bda970ce6a91d81f48fc72aa2457586a076f
Signed-off-by: Filip Varga <fivarga@cisco.com>
diff --git a/src/vnet/buffer.h b/src/vnet/buffer.h
index 50515c4..9e997b8 100644
--- a/src/vnet/buffer.h
+++ b/src/vnet/buffer.h
@@ -452,11 +452,10 @@
   /* size of L4 prototol header */
   u16 gso_l4_hdr_sz;
 
-  /* The union below has a u64 alignment, so this space is unused */
-  u32 __unused2[1];
-
   struct
   {
+    u16 unused;
+    u16 thread_next;
     u32 arc_next;
     u32 ed_out2in_nat_session_index;
   } nat;