TOMOYO: Change list iterator.

Change list_for_each_cookie to

(1) start from current position rather than next position
(2) remove temporary cursor
(3) check that srcu_read_lock() is held

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>