net: fix bogus errno reporting

_listen2() emits the error on the next tick. The errno value may have changed
by then.

lib/net.js

@@ -911,10 +911,11 @@ Server.prototype._listen2 = function(address, port, addressType, backlog, fd) {
   r = self._handle.listen(backlog || 511);
 
   if (r) {
+    var ex = errnoException(errno, 'listen');
     self._handle.close();
     self._handle = null;
     process.nextTick(function() {
-      self.emit('error', errnoException(errno, 'listen'));
+      self.emit('error', ex);
     });
     return;
   }