dgram: prevent disabled optimization of bind()

Reassigning a named parameter while also using the arguments
object causes the entire function to never be optimized.

PR-URL: https://github.com/nodejs/node/pull/4613
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/dgram.js

@@ -134,8 +134,9 @@ function replaceHandle(self, newHandle) {
   self._handle = newHandle;
 }
 
-Socket.prototype.bind = function(port /*, address, callback*/) {
+Socket.prototype.bind = function(port_ /*, address, callback*/) {
   var self = this;
+  let port = port_;
 
   self._healthCheck();