io_uring: don't disable kiocb_done() CQE batching

Not passing issue_flags from kiocb_done() into __io_complete_rw() means
that completion batching for this case is disabled, e.g. for most of
buffered reads.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b2689462835c3ee28a5999ef4f9a581e24be04a2.1630539342.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2656,7 +2656,7 @@ static void __io_complete_rw(struct io_kiocb *req, long res, long res2,
 {
 	if (__io_complete_rw_common(req, res))
 		return;
-	__io_req_complete(req, 0, req->result, io_put_rw_kbuf(req));
+	__io_req_complete(req, issue_flags, req->result, io_put_rw_kbuf(req));
 }
 
 static void io_complete_rw(struct kiocb *kiocb, long res, long res2)