fix isDefaultGateway wrong doc

[arthur-zhang]

isDefaultGateway belongs to bridge delegate, not ipam.

the following is right:

{
  "cniVersion": "1.0.0",
  "name": "cni0",
  "type": "flannel",
  "subnetFile": "/var/run/flannel/subnet.env",
  "dataDir": "/tmp/flannel/",
  "delegate":{
          "isDefaultGateway":true
  }
}

however, if we change to ipam, it will not work

[manuelbuil]

Thanks

[manuelbuil]

Thanks for contributing. You have a point but I would rephrase it because delegate configuration does not make much sense. What about this:

Additionally, for the bridge plugin, `isGateway` will be set to `true`, if not present. The bridge plugin includes ``isDefaultGateway` that when false allow adding back the routes to the cluster services and/or to the hosts. In that case, the bridge plugin does not install a default route and, as a result, only pod-to-pod connectivity would be available.