rbd: send header version when notifying

Previously the original header version was sent. Now, we update it
when the header changes.

Signed-off-by: Josh Durgin <josh.durgin@dreamhost.com>
Reviewed-by: Alex Elder <elder@inktank.com>
(cherry picked from commit a71b891bc7d77a070e723c8c53d1dd73cf931555)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>