os/bluestore/KernelDevice: fix RW_IO_MAX constant
This depends on the page size. See:
https://github.com/torvalds/linux/blob/
6e6d05360b80f196ed07061327f03346b204abea/include/linux/fs.h#L2305
https://github.com/torvalds/linux/blob/
30d1d92a888d03681b927c76a35181b4eed7071f/tools/virtio/linux/kernel.h#L23
Fixes
4d33114a40d5ae0d541c36175977ca22789a3b88
Fixes: https://tracker.ceph.com/issues/41188
Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit
6f7179daa6c17907f8fe38150183008e2d096109)