dgram: change 'this' to 'self' for 'isConnected'

The function 'isConnected' is directly called by many 'Socket' instance,
so we shouldn't directly use 'this' because 'this' will be the self of
function itself, and we should use 'self' as the instance of 'Socket'
function.

PR-URL: #27338
Reviewed-By: Santiago Gimeno <[email protected]>
Reviewed-By: Joyee Cheung <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Franziska Hinkelmann <[email protected]>
Reviewed-By: Yongsheng Zhang <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>

lib/dgram.js

@@ -519,7 +519,7 @@ function clearQueue() {
 
 function isConnected(self) {
   try {
-    this.remoteAddress();
+    self.remoteAddress();
     return true;
   } catch {
     return false;