rbd: set max_sectors explicitly

Commit 30e2bc08 ("Revert "block: remove artifical max_hw_sectors
cap"") restored a clamp on max_sectors.  It's now 2560 sectors instead
of 1024, but it's not good enough: we set max_hw_sectors to rbd object
size because we don't want object sized I/Os to be split, and the
default object size is 4M.

So, set max_sectors to max_hw_sectors in rbd at queue init time.
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Alex Elder <elder@linaro.org>

drivers/block/rbd.c

@@ -3760,6 +3760,7 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
 	/* set io sizes to object size */
 	segment_size = rbd_obj_bytes(&rbd_dev->header);
 	blk_queue_max_hw_sectors(q, segment_size / SECTOR_SIZE);
+	q->limits.max_sectors = queue_max_hw_sectors(q);
 	blk_queue_max_segments(q, segment_size / SECTOR_SIZE);
 	blk_queue_max_segment_size(q, segment_size);
 	blk_queue_io_min(q, segment_size);