net/sched: act_ct: Instantiate flow table entry actions

NF flow table API associate 5-tuple rule with an action list by calling
the flow table type action() CB to fill the rule's actions.

In action CB of act_ct, populate the ct offload entry actions with a new
ct_metadata action. Initialize the ct_metadata with the ct mark, label and
zone information. If ct nat was performed, then also append the relevant
packet mangle actions (e.g. ipv4/ipv6/tcp/udp header rewrites).

Drivers that offload the ft entries may match on the 5-tuple and perform
the action list.

Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>