core: Inode: Improve forFileIdKey and innerInode

Now that we have a Opaque-specific constructor, let's use it instead of
converting back and forth from byte[].

Related: #149
Signed-off-by: Christian Kohlschütter <[email protected]>

Author: kohlschuetter

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

@@ -147,11 +147,11 @@ public static Inode forFile(byte[] bytes) {
     }
 
     public static Inode forFileIdKey(Opaque key) {
-        return forFile(key.toBytes());
+        return new Inode(0, 0, 0, key);
     }
 
     public static Inode innerInode(Inode outerInode) {
-        return new Inode(0, 0, 0, outerInode.getFileIdKey());
+        return forFileIdKey(outerInode.getFileIdKey());
     }
 
     @Deprecated(forRemoval = true)