netfilter: nft_meta: add l4proto support

For L3-proto independant rules we need to get at the L4 protocol value
directly. Add it to the nft_pktinfo struct and use the meta expression
to retrieve it.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -532,6 +532,7 @@ enum nft_exthdr_attributes {
  * @NFT_META_RTCLASSID: realm value of packet's route (skb->dst->tclassid)
  * @NFT_META_SECMARK: packet secmark (skb->secmark)
  * @NFT_META_NFPROTO: netfilter protocol
+ * @NFT_META_L4PROTO: layer 4 protocol number
  */
 enum nft_meta_keys {
 	NFT_META_LEN,
@@ -550,6 +551,7 @@ enum nft_meta_keys {
 	NFT_META_RTCLASSID,
 	NFT_META_SECMARK,
 	NFT_META_NFPROTO,
+	NFT_META_L4PROTO,
 };
 
 /**