io_uring: indicate if io_kbuf_recycle did recycle anything

It can be useful to know if io_kbuf_recycle did actually recycle the
buffer on the request, or if it left the request alone.

Signed-off-by: Dylan Yudaken <dyudaken@gmail.com>
Link: https://lore.kernel.org/r/20231106203909.197089-2-dyudaken@gmail.com


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