tc: jsonify nat action

tc: jsonify nat action

Add json output support for nat action

Example output:

~$ $TC actions add action nat egress 10.10.10.1 20.20.20.2 index 2
~$ $TC actions add action nat ingress 100.100.100.1/32 200.200.200.2 \
	continue index 99
~$ $TC -j actions ls action nat

[{
	"total acts": 2
}, {
	"actions": [{
		"order": 0,
		"type": "nat",
		"direction": "egress",
		"old_addr": "10.10.10.1/32",
		"new_addr": "20.20.20.2",
		"control_action": {
			"type": "pass"
		},
		"index": 2,
		"ref": 1,
		"bind": 0
	}, {
		"order": 1,
		"type": "nat",
		"direction": "ingress",
		"old_addr": "100.100.100.1/32",
		"new_addr": "200.200.200.2",
		"control_action": {
			"type": "continue"
		},
		"index": 99,
		"ref": 1,
		"bind": 0
	}]
}]

Signed-off-by: Keara Leibovitz <kleib@mojatatu.com>
Signed-off-by: David Ahern <dsahern@gmail.com>