vfs: make file handle immutable class

no reasons not to.

Acked-by: Marina Sahakyan
Target: master

Author: kofemann

core/src/main/java/org/dcache/nfs/vfs/Inode.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2009 - 2019 Deutsches Elektronen-Synchroton,
+ * Copyright (c) 2009 - 2024 Deutsches Elektronen-Synchroton,
  * Member of the Helmholtz Association, (DESY), HAMBURG, GERMANY
  *
  * This library is free software; you can redistribute it and/or modify
@@ -23,7 +23,7 @@
 
 public class Inode {
 
-    FileHandle fh;
+    private final FileHandle fh;
 
     public Inode(byte[] bytes) {
         this(new FileHandle(bytes));