fhandle: raise FILEID_IS_DIR in handle_type

Currently FILEID_IS_DIR is raised in fh_flags which is wrong.
Raise it in handle->handle_type were it's supposed to be.

Link: https://lore.kernel.org/20250624-work-pidfs-fhandle-v2-1-d02a04858fe3@kernel.org


Fixes: c374196b ("fs: name_to_handle_at() support for "explicit connectable" file handles")
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>