Add support for ICMP extensions in reports

[fujiapple852]

Show ICMP extensions in json and stream reports. No support for "flat" reports csv, pretty or md. Not applicable to silent, flows or dot.

Json:

{
  "ttl": 11,
  "hosts": [
    {
      "ip": "129.250.2.50",
      "hostname": "ae-10.r32.tokyjp05.jp.bb.gin.ntt.net"
    }
  ],
  "extensions": [
    {
      "mpls": {
        "members": [
          {
            "label": 48268,
            "exp": 0,
            "bos": 1,
            "ttl": 1
          }
        ]
      }
    }
  ],
  "loss_pct": "0.00",
  "sent": 1,
  "last": "62.67",
  "recv": 1,
  "avg": "62.67",
  "best": "62.67",
  "worst": "62.67",
  "stddev": "0.00"
}

Stream:

ttl=11 addrs=129.250.2.50 exts=mpls(labels=48268) loss_pct=0.0 sent=1 recv=1 last=62.8 best=62.8 worst=62.8 avg=62.8 stddev=0.0