Fix webhook panic error caused by bumping controller-runtime

The controller-manager won't automatically inject decoder to webhook handler in new implementation, which
will cause the panic error of webhook. Use admission.NewDecoder(scheme) instead as it is now the only way
to instantiate default decoder.

kubernetes-sigs/controller-runtime#2736

pkg/controllers/subnetset/subnetset_controller.go

@@ -19,9 +19,9 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/controller"
 	"sigs.k8s.io/controller-runtime/pkg/controller/controllerutil"
 	"sigs.k8s.io/controller-runtime/pkg/webhook"
+	"sigs.k8s.io/controller-runtime/pkg/webhook/admission"
 
 	"github.com/vmware-tanzu/nsx-operator/pkg/apis/v1alpha1"
-
 	"github.com/vmware-tanzu/nsx-operator/pkg/config"
 	"github.com/vmware-tanzu/nsx-operator/pkg/controllers/common"
 	"github.com/vmware-tanzu/nsx-operator/pkg/logger"
@@ -343,7 +343,10 @@ func (r *SubnetSetReconciler) Start(mgr ctrl.Manager, enableWebhook bool) error
 		}
 		hookServer.Register("/validate-nsx-vmware-com-v1alpha1-subnetset",
 			&webhook.Admission{
-				Handler: &SubnetSetValidator{Client: mgr.GetClient()},
+				Handler: &SubnetSetValidator{
+					Client:  mgr.GetClient(),
+					decoder: admission.NewDecoder(mgr.GetScheme()),
+				},
 			})
 	}
 	go r.GarbageCollector(make(chan bool), servicecommon.GCInterval)

pkg/controllers/subnetset/subnetset_webhook.go

@@ -103,10 +103,3 @@ func (v *SubnetSetValidator) Handle(ctx context.Context, req admission.Request)
 	}
 	return admission.Allowed("")
 }
-
-// InjectDecoder injects the decoder into a validator.
-// A decoder will be automatically injected by controller-manager.
-func (v *SubnetSetValidator) InjectDecoder(d *admission.Decoder) error {
-	v.decoder = d
-	return nil
-}