Improve DFSUtil#checkProtectedDescendants() related parameter comments

Some parameter comments related to DFSUtil#checkProtectedDescendants() are missing, for example:
/**

• If the given directory has any non-empty protected descendants, throw
• (Including itself).
  *
• @param iip directory, to check its descendants.
• @throws AccessControlException if it is a non-empty protected descendant
• found.
• @throws ParentNotDirectoryException
• @throws UnresolvedLinkException
  */
  public static void checkProtectedDescendants(
  FSDirectory fsd, INodesInPath iip)
  Throw AccessControlException, UnresolvedLinkException,
  ParentNotDirectoryException {
  The description of fsd is missing here.