bgpd: fix show bgp l2vpn evpn route json

bgpd: fix show bgp l2vpn evpn route json

PR-4544 has introduced a new filed extended community
in show bgp l2vpn evpn route command.
The header has missed checking json is enabled.

Ticket:CM-25581
Reviewed By:
Testing Done:

TORS1# show bgp l2vpn evpn route json
{
  "27.0.0.15:8":{
    "rd":"27.0.0.15:8",
    "[2]:[0]:[48]:[00:02:00:00:00:0a]":{
      "prefix":"[2]:[0]:[48]:[00:02:00:00:00:0a]",
      "prefixLen":288,
      "paths":[
        [
          {
            "valid":true,
            "bestpath":true,
            "pathFrom":"external",
            "routeType":2,
            "ethTag":0,
            "macLen":48,
            "mac":"00:02:00:00:00:0a",
            "weight":32768,
            "peerId":"(unspec)",
            "aspath":"",
            "path":"",
            "origin":"IGP",
            "extendedCommunity":{
              "string":"ET:8 RT:5550:1002"
            },
            "nexthops":[
              {
                "ip":"27.0.0.15",
                "afi":"ipv4",
                "used":true
              }
            ]
          }
        ]
      ]
    },
   ...
  },
  "numPrefix":187,
  "numPaths":343
}

Signed-off-by: Chirag Shah <chirag@cumulusnetworks.com>