ip: link_gre6.c: add json output support

ip: link_gre6.c: add json output support

Schema
{
    "remote": {
        "type": "string",
        "attr": "IFLA_GRE_REMOTE"
    },
    "local": {
        "type": "string",
        "attr": "IFLA_GRE_LOCAL"
    },
    "link": {
        "type": "string",
        "attr": "IFLA_GRE_LINK",
        "mutually_exclusive": {
            "link_index": {
                "type": "uint",
            }
        }
    },
    "ttl": {
        "type": "int",
        "attr": "IFLA_GRE_TTL"
    },
    "ip6_tnl_f_ign_encap_limit": {
        "type": "bool",
        "attr": "IP6_TNL_F_IGN_ENCAP_LIMIT"
    },
    "encap_limit": {
        "type": "int",
        "attr": "IFLA_GRE_ENCAP_LIMIT"
    },
    "ip6_tnl_f_use_orig_flowlabel": {
        "type": "bool",
        "attr": "IP6_TNL_F_USE_ORIG_FLOWLABEL"
    },
    "flowlabel": {
        "type": "string",
        "attr": "IP6_FLOWINFO_FLOWLABEL"
    },
    "ip6_tnl_f_rcv_dscp_copy": {
        "type": "bool",
        "attr": "IP6_TNL_F_RCV_DSCP_COPY"
    },
    "ikey": {
        "type": "string",
        "attr": "IFLA_GRE_IKEY"
    },
    "okey": {
        "type": "string",
        "attr": "IFLA_GRE_OKEY"
    },
    "iseq": {
        "type": "bool",
        "attr": "IFLA_GRE_IFLAGS & GRE_SEQ"
    },
    "oseq": {
        "type": "bool",
        "attr": "IFLA_GRE_OFLAGS & GRE_SEQ"
    },
    "icsum": {
        "type": "bool",
        "attr": "IFLA_GRE_IFLAGS & GRE_CSUM"
    },
    "ocsum": {
        "type": "bool",
        "attr": "IFLA_GRE_OFLAGS & GRE_CSUM"
    },
    "encap": {
        "type": "dict",
        "attr": "IFLA_GRE_ENCAP_TYPE != TUNNEL_ENCAP_NONE",
        "dict": {
            "type": {
                "type": "string",
                "attr": "IFLA_GRE_ENCAP_TYPE"
            },
            "sport": {
                "type": "uint",
                "attr": "IFLA_GRE_ENCAP_SPORT"
            },
            "dport": {
                "type": "uint",
                "attr": "IFLA_GRE_ENCAP_DPORT"
            },
            "csum": {
                "type": "bool",
                "attr": "TUNNEL_ENCAP_FLAG_CSUM"
            },
            "csum6": {
                "type": "bool",
                "attr": "TUNNEL_ENCAP_FLAG_CSUM6"
            },
            "remcsum": {
                "type": "bool",
                "attr": "TUNNEL_ENCAP_FLAG_REMCSUM"
            }
        }
    }
}

$ ip link show
$ ip -6 tunnel add name tun6 mode ip6gre local 2001:db8:1::1/64 remote
2001:0db8:85a3:0000:0000:8a2e:0370:7334
$ ip link show
10: ip6tnl0@NONE: <NOARP> mtu 1452 qdisc noop state DOWN mode DEFAULT
group default
    link/tunnel6 :: brd ::
11: ip6gre0@NONE: <NOARP> mtu 1448 qdisc noop state DOWN mode DEFAULT
group default
    link/gre6 00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00 brd
00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00
12: tun6@NONE: <POINTOPOINT,NOARP> mtu 1448 qdisc noop state DOWN mode
DEFAULT group default
    link/gre6 20:01:0d:b8:00:01:00:00:00:00:00:00:00:00:00:01 peer
20:01:0d:b8:85:a3:00:00:00:00:8a:2e:03:70:73:34
➜  ~ ./ip -details -json link show
[{
        "ifindex": 10,
        "ifname": "ip6tnl0",
        "link": null,
        "flags": ["NOARP"],
        "mtu": 1452,
        "qdisc": "noop",
        "operstate": "DOWN",
        "linkmode": "DEFAULT",
        "group": "default",
        "link_type": "tunnel6",
        "address": "::",
        "broadcast": "::",
        "promiscuity": 0,
        "linkinfo": {
            "info_kind": "ip6tnl",
            "info_data": {
                "proto": "ip6ip6",
                "remote": "::",
                "local": "::",
                "encap_limit": 0,
                "ttl": 0,
                "flowinfo_tclass": "0x00",
                "flowlabel": "0x00000",
                "flowinfo": "0x00000000"
            }
        },
        "inet6_addr_gen_mode": "eui64",
        "num_tx_queues": 1,
        "num_rx_queues": 1,
        "gso_max_size": 65536,
        "gso_max_segs": 65535
    },{
        "ifindex": 11,
        "ifname": "ip6gre0",
        "link": null,
        "flags": ["NOARP"],
        "mtu": 1448,
        "qdisc": "noop",
        "operstate": "DOWN",
        "linkmode": "DEFAULT",
        "group": "default",
        "link_type": "gre6",
        "address": "00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00",
        "broadcast": "00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00",
        "promiscuity": 0,
        "linkinfo": {
            "info_kind": "ip6gre",
            "info_data": {
                "remote": "any",
                "local": "any",
                "ttl": 0,
                "encap_limit": 0,
                "flowlabel": "0x00000"
            }
        },
        "inet6_addr_gen_mode": "eui64",
        "num_tx_queues": 1,
        "num_rx_queues": 1,
        "gso_max_size": 65536,
        "gso_max_segs": 65535
    },{
        "ifindex": 12,
        "ifname": "tun6",
        "link": null,
        "flags": ["POINTOPOINT","NOARP"],
        "mtu": 1448,
        "qdisc": "noop",
        "operstate": "DOWN",
        "linkmode": "DEFAULT",
        "group": "default",
        "link_type": "gre6",
        "address": "20:01:0d:b8:00:01:00:00:00:00:00:00:00:00:00:01",
        "link_pointtopoint": true,
        "broadcast": "20:01:0d:b8:85:a3:00:00:00:00:8a:2e:03:70:73:34",
        "promiscuity": 0,
        "linkinfo": {
            "info_kind": "ip6gre",
            "info_data": {
                "remote": "2001:db8:85a3::8a2e:370:7334",
                "local": "2001:db8:1::1",
                "ttl": 64,
                "encap_limit": 4,
                "flowlabel": "0x00000"
            }
        },
        "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>