Include correct duped value in DefaultResourceLeak.toString() (#8413)

Motivation:

DefaultResourceLeak.toString() did include the wrong value for duplicated records.

Modifications:

Include the correct value.

Result:

Correct toString() implementation.

common/src/main/java/io/netty/util/ResourceLeakDetector.java

@@ -501,7 +501,7 @@ public class ResourceLeakDetector<T> {
 
             if (duped > 0) {
                 buf.append(": ")
-                        .append(dropped)
+                        .append(duped)
                         .append(" leak records were discarded because they were duplicates")
                         .append(NEWLINE);
             }