[NETFILTER]: x_tables: add TRACE target

The TRACE target can be used to follow IP and IPv6 packets through
the ruleset.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick NcHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 2d6a14f..625d73b 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -227,6 +227,7 @@
  *	@mark: Generic packet mark
  *	@nfct: Associated connection, if any
  *	@ipvs_property: skbuff is owned by ipvs
+ *	@nf_trace: netfilter packet trace flag
  *	@nfctinfo: Relationship of this skb to the connection
  *	@nfct_reasm: netfilter conntrack re-assembly pointer
  *	@nf_bridge: Saved data about a bridged frame - see br_netfilter.c
@@ -278,7 +279,8 @@
 				nfctinfo:3;
 	__u8			pkt_type:3,
 				fclone:2,
-				ipvs_property:1;
+				ipvs_property:1,
+				nf_trace:1;
 	__be16			protocol;
 
 	void			(*destructor)(struct sk_buff *skb);