pimd: JSON support for "show ip mroute"

pimd: JSON support for "show ip mroute"

Signed-off-by: Daniel Walton <dwalton@cumulusnetworks.com>
Ticket: CM-12876

root@superm-redxp-05[pimd]# vtysh -c 'show ip mroute json' | pjson
{
  "230.10.10.1": {
    "20.0.13.253": {
      "br1": {
        "swp1": {
          "group": "230.10.10.1",
          "iVifI": 1,
          "inboundInterface": "br1",
          "oVifI": 2,
          "outboundInterface": "swp1",
          "protocolPim": true,
          "source": "20.0.13.253",
          "ttl": 1,
          "upTime": "00:02:37"
        }
      }
    }
  },
  "230.10.10.4": {
    "20.0.13.253": {
      "br1": {}
    }
  }
}
root@superm-redxp-05[pimd]#