ip: iplink_vxlan.c: add json output support

ip: iplink_vxlan.c: add json output support

Schema:
{
    "id": {
        "type": "uint",
        "attr": "IFLA_VXLAN_ID"
    },
    "group": {
        "type": "string",
        "attr": "IFLA_VXLAN_GROUP"
    },
    "remote": {
        "type": "string",
        "attr": "IFLA_VXLAN_GROUP"
    },
    "group6": {
        "type": "string",
        "attr": "IFLA_VXLAN_GROUP6"
    },
    "remote6": {
        "type": "string",
        "attr": "IFLA_VXLAN_GROUP6"
    },
    "local": {
        "type": "string",
        "attr": "IFLA_VXLAN_LOCAL"
    },
    "local6": {
        "type": "string",
        "attr": "IFLA_VXLAN_LOCAL6"
    },
    "link": {
        "type": "string",
        "attr": "IFLA_VXLAN_LINK",
        "mutually_exclusive": {
            "link_index": {
                "type": "uint",
                "comment": "if not ifname for ifindex"
            }
        }
    },
    "port_range": {
        "type": "dict",
        "attr": "IFLA_VXLAN_PORT_RANGE",
        "dict": {
            "low": {
                "type": "uint"
            },
            "high": {
                "type": "uint"
            }
        }
    },
    "port": {
        "type": "uint",
        "attr": "IFLA_VXLAN_PORT"
    },
    "learning": {
        "type": "bool",
        "attr": "IFLA_VXLAN_LEARNING"
    },
    "proxy": {
        "type": "bool",
        "attr": "IFLA_VXLAN_PROXY"
    },
    "rsc": {
        "type": "bool",
        "attr": "IFLA_VXLAN_RSC"
    },
    "l2miss": {
        "type": "bool",
        "attr": "IFLA_VXLAN_L2MISS"
    },
    "l3miss": {
        "type": "bool",
        "attr": "IFLA_VXLAN_L3MISS"
    },
    "tos": {
        "type": "string",
        "attr": "IFLA_VXLAN_TOS"
    },
    "ttl": {
        "type": "int",
        "attr": "IFLA_VXLAN_TTL"
    },
    "label": {
        "type": "string",
        "attr": "IFLA_VXLAN_LABEL"
    },
    "ageing": {
        "type": "uint",
        "attr": "IFLA_VXLAN_AGEING"
    },
    "limit": {
        "type": "uint",
        "attr": "IFLA_VXLAN_LIMIT"
    },
    "udp_csum": {
        "type": "bool",
        "attr": "IFLA_VXLAN_UDP_CSUM"
    },
    "udp_zero_csum6_tx": {
        "type": "bool",
        "attr": "IFLA_VXLAN_UDP_ZERO_CSUM6_TX"
    },
    "udp_zero_csum6_rx": {
        "type": "bool",
        "attr": "IFLA_VXLAN_UDP_ZERO_CSUM6_RX"
    },
    "remcsum_tx": {
        "type": "bool",
        "attr": "IFLA_VXLAN_REMCSUM_TX"
    },
    "remcsum_rx": {
        "type": "bool",
        "attr": "IFLA_VXLAN_REMCSUM_RX"
    },
    "collect_metadata": {
        "type": "bool",
        "attr": "IFLA_VXLAN_COLLECT_METADATA"
    },
    "gbp": {
        "type": "bool",
        "attr": "IFLA_VXLAN_GBP"
    },
    "gpe": {
        "type": "bool",
        "attr": "IFLA_VXLAN_GPE"
    }
}

$ ip link add name vxlan42 type vxlan id 42 dev eth0 remote 203.0.113.6
local 192.0.2.1 dstport 4789
$ ip link add name vxlan43 type vxlan id 43 dev eth0 group 239.0.0.1
dstport 4789
$ ip -details -json link show
[{
        "ifindex": 17,
        "ifname": "vxlan42",
        "flags": ["BROADCAST","MULTICAST"],
        "mtu": 1450,
        "qdisc": "noop",
        "operstate": "DOWN",
        "linkmode": "DEFAULT",
        "group": "default",
        "link_type": "ether",
        "address": "b2:92:0e:1a:c6:42",
        "broadcast": "ff:ff:ff:ff:ff:ff",
        "promiscuity": 0,
        "linkinfo": {
            "info_kind": "vxlan",
            "info_data": {
                "id": 42,
                "remote": "203.0.113.6",
                "local": "192.0.2.1",
                "link": "eth0",
                "port_range": {
                    "low": 0,
                    "high": 0
                },
                "port": 4789,
                "learning": true,
                "ttl": 0,
                "ageing": 300,
                "udp_csum": false,
                "udp_zero_csum6_tx": false,
                "udp_zero_csum6_rx": false
            }
        },
        "inet6_addr_gen_mode": "eui64",
        "num_tx_queues": 1,
        "num_rx_queues": 1,
        "gso_max_size": 65536,
        "gso_max_segs": 65535
    },{
        "ifindex": 18,
        "ifname": "vxlan43",
        "flags": ["BROADCAST","MULTICAST"],
        "mtu": 1450,
        "qdisc": "noop",
        "operstate": "DOWN",
        "linkmode": "DEFAULT",
        "group": "default",
        "link_type": "ether",
        "address": "c6:51:4d:7f:f9:2f",
        "broadcast": "ff:ff:ff:ff:ff:ff",
        "promiscuity": 0,
        "linkinfo": {
            "info_kind": "vxlan",
            "info_data": {
                "id": 43,
                "group": "239.0.0.1",
                "link": "eth0",
                "port_range": {
                    "low": 0,
                    "high": 0
                },
                "port": 4789,
                "learning": true,
                "ttl": 0,
                "ageing": 300,
                "udp_csum": false,
                "udp_zero_csum6_tx": false,
                "udp_zero_csum6_rx": false
            }
        },
        "inet6_addr_gen_mode": "eui64",
        "num_tx_queues": 1,
        "num_rx_queues": 1,
        "gso_max_size": 65536,
        "gso_max_segs": 65535
    }
]

Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>