io_uring: cancel not-armed linked touts separately

Adjust io_disarm_next(), so it can detect if there is a linked but
not-yet-armed timeout and complete/cancel it separately. Will be used in
the following patch.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/ae228cde2c0df3d92d29d5e4852ed9fa8a2a97db.1628981736.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>