io_uring: allow multishot polled reqs to defer completion

Until now there was no reason for multishot polled requests to defer
completions as there was no functional difference. However now this will
actually defer the completions, for a performance win.

Signed-off-by: Dylan Yudaken <dylany@meta.com>
Link: https://lore.kernel.org/r/20221124093559.3780686-10-dylany@meta.com


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