rdma: Implement json output for dev object

rdma: Implement json output for dev object

The example output for machine with two devices

root@mtr-leonro:~# rdma dev -j -p
[{
	"ifindex": 1,
	"ifname": "mlx5_0",
	"node_type": "ca",
	"fw": "2.8.9999",
	"node_guid": "5254:00c0:fe12:3457",
	"sys_image_guid": 5254:00c0:fe12:3457",
	"caps": [ "BAD_PKEY_CNTR", "BAD_QKEY_CNTR", "CHANGE_PHY_POR",
		  "PORT_ACTIVE_EVENT", "SYS_IMAGE_GUID", "RC_RNR_NAK_GEN",
		  "MEM_WINDOW", "UD_IP_CSUM", "UD_TSO", "XRC",
		  "MEM_MGT_EXTENSIONS", "BLOCK_MULTICAST_LOOPBACK",
		  "MEM_WINDOW_TYPE_2B", "RAW_IP_CSUM",
		  "MANAGED_FLOW_STEERING", "RESIZE_MAX_WR" ]
	},{
	"ifindex": 2,
	"ifname": mlx5_1,
	"node_type": "ca",
	"fw": "2.8.9999",
	"node_guid": "5254:00c0:fe12:3458",
	"sys_image_guid": "5254:00c0:fe12:3458",
	"caps": [ "BAD_PKEY_CNTR", "BAD_QKEY_CNTR", "CHANGE_PHY_POR",
		  "PORT_ACTIVE_EVENT", "SYS_IMAGE_GUID", "RC_RNR_NAK_GEN",
		  "MEM_WINDOW", "UD_IP_CSUM", "UD_TSO", "XRC",
		  "MEM_MGT_EXTENSIONS", "BLOCK_MULTICAST_LOOPBACK",
		  "MEM_WINDOW_TYPE_2B", "RAW_IP_CSUM",
		  "MANAGED_FLOW_STEERING", "RESIZE_MAX_WR" ]
	}
]

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>