io_uring/poll: disable level triggered poll

Stefan reports that there are issues with the level triggered
notification. Since we're late in the cycle, and it was introduced for
the 6.0 release, just disable it at prep time and we can bring this
back when Samba is happy with it.

Reported-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>