Fix the GatewayClass default Condition

[jbdoumenjou]

What happened:

Create a GatewayClass object and have the following default condition:

{
  "conditions": [
    {
      "lastTransitionTime": "1970-01-01T00:00:00Z",
      "message": "Waiting for controller",
      "reason": "Waiting",
      "status": "Unknown",
      "type": "InvalidParameters"
    }
  ]
}

What you expected to happen:
According to #466

{
  "conditions": [
    {
      "lastTransitionTime": "1970-01-01T00:00:00Z",
      "message": "Waiting for controller",
      "reason": "Waiting",
      "status": "False",
      "type": "Admitted"
    }
  ]
}

How to reproduce it (as minimally and precisely as possible):

kubectl apply -f config/crd/bases/
kubectl apply -f examples/basic-http.yaml
kubectl get -o json gatewayclasses/acme-lb | jq .status