Add missing watch error handler for ingress class informer (istio#37408)

Author: SpecialYang

pilot/pkg/config/kube/ingress/controller.go

@@ -297,6 +297,11 @@ func (c *controller) SetWatchErrorHandler(handler func(r *cache.Reflector, err e
 	if err := c.ingressInformer.SetWatchErrorHandler(handler); err != nil {
 		errs = multierror.Append(err, errs)
 	}
+	if c.classes != nil {
+		if err := c.classes.Informer().SetWatchErrorHandler(handler); err != nil {
+			errs = multierror.Append(err, errs)
+		}
+	}
 	return errs
 }
 

pilot/pkg/config/kube/ingressv1/controller.go

@@ -250,6 +250,9 @@ func (c *controller) SetWatchErrorHandler(handler func(r *cache.Reflector, err e
 	if err := c.ingressInformer.SetWatchErrorHandler(handler); err != nil {
 		errs = multierror.Append(err, errs)
 	}
+	if err := c.classes.Informer().SetWatchErrorHandler(handler); err != nil {
+		errs = multierror.Append(err, errs)
+	}
 	return errs
 }