netfilter: meta: secpath support

replacement for iptables "-m policy --dir in --policy {ipsec,none}".

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -777,6 +777,7 @@ enum nft_exthdr_attributes {
  * @NFT_META_OIFGROUP: packet output interface group
  * @NFT_META_CGROUP: socket control group (skb->sk->sk_classid)
  * @NFT_META_PRANDOM: a 32bit pseudo-random number
+ * @NFT_META_SECPATH: boolean, secpath_exists (!!skb->sp)
  */
 enum nft_meta_keys {
 	NFT_META_LEN,
@@ -804,6 +805,7 @@ enum nft_meta_keys {
 	NFT_META_OIFGROUP,
 	NFT_META_CGROUP,
 	NFT_META_PRANDOM,
+	NFT_META_SECPATH,
 };
 
 /**