net_legacy: Fix throw typo

Thanks Tobi

lib/net_legacy.js

@@ -1073,7 +1073,7 @@ Server.prototype.listen = function() {
         if (err.errno == ENOENT) {
           self._doListen(path);
         } else {
-          throw r;
+          throw err;
         }
       } else {
         if (!r.isSocket()) {