attach: use free_disarm()

src/lxc/attach.c

@@ -109,8 +109,7 @@ static inline void lxc_proc_close_ns_fd(struct lxc_proc_context_info *ctx)
 
 static void lxc_proc_put_context_info(struct lxc_proc_context_info *ctx)
 {
-	free(ctx->lsm_label);
-	ctx->lsm_label = NULL;
+	free_disarm(ctx->lsm_label);
 
 	if (ctx->container) {
 		lxc_container_put(ctx->container);