fix'--log-file only works if --logtostderr=false'

cmd/kubeadm/app/apis/kubeadm/validation/validation.go

@@ -568,7 +568,7 @@ func isAllowedFlag(flagName string) bool {
 		kubeadmcmdoptions.KubeconfigDir,
 		kubeadmcmdoptions.UploadCerts,
 		kubeadmcmdoptions.Patches,
-		"print-join-command", "rootfs", "v")
+		"print-join-command", "rootfs", "v", "log-file")
 	if allowedFlags.Has(flagName) {
 		return true
 	}