netfilter: ipset: add hash:ip,mark data type to ipset

Introduce packet mark support with new ip,mark hash set. This includes
userspace and kernelspace code, hash:ip,mark set tests and man page
updates.

The intended use of ip,mark set is similar to the ip:port type, but for
protocols which don't use a predictable port number. Instead of port
number it matches a firewall mark determined by a layer 7 filtering
program like opendpi.

As well as allowing or blocking traffic it will also be used for
accounting packets and bytes sent for each protocol.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>

include/uapi/linux/netfilter/ipset/ip_set.h

@@ -82,6 +82,7 @@ enum {
 	IPSET_ATTR_PROTO,	/* 7 */
 	IPSET_ATTR_CADT_FLAGS,	/* 8 */
 	IPSET_ATTR_CADT_LINENO = IPSET_ATTR_LINENO,	/* 9 */
+	IPSET_ATTR_MARK,	/* 10 */
 	/* Reserve empty slots */
 	IPSET_ATTR_CADT_MAX = 16,
 	/* Create-only specific attributes */