ipsec: fix IPv6 IPsec tunnel punting

Type: fix
Buffer needs to be rewinded before being passed to punt-dispatch node.

Change-Id: I43d103515d372e425f4c3b08ca1779398f1fced4
Signed-off-by: Sylvain Cadilhac <sylvain.cadilhac@freepro.com>
diff --git a/src/vnet/ipsec/ipsec_tun_in.c b/src/vnet/ipsec/ipsec_tun_in.c
index 9f1e2d6..a419d8c 100644
--- a/src/vnet/ipsec/ipsec_tun_in.c
+++ b/src/vnet/ipsec/ipsec_tun_in.c
@@ -278,6 +278,7 @@
 	      else
 		{
 		  next[0] = ipsec_ip6_if_no_tunnel (node, b[0], esp0, ip60);
+		  vlib_buffer_advance (b[0], -buf_rewind0);
 		  n_no_tunnel++;
 		  goto trace00;
 		}