fix LedgerHandle ensembleChangeCounter not used. (apache#4103)

### Motivation
fix apache#4096

ensemble change counter not inc when ensemble change .

### Changes
inc counter when ensemble change.

bookkeeper-server/src/main/java/org/apache/bookkeeper/client/LedgerHandle.java

@@ -1913,6 +1913,7 @@ void handleBookieFailure(final Map<Integer, BookieId> failedBookies) {
 
     void ensembleChangeLoop(List<BookieId> origEnsemble, Map<Integer, BookieId> failedBookies) {
         int ensembleChangeId = numEnsembleChanges.incrementAndGet();
+        ensembleChangeCounter.inc();
         String logContext = String.format("[EnsembleChange(ledger:%d, change-id:%010d)]", ledgerId, ensembleChangeId);
 
         // when the ensemble changes are too frequent, close handle