dirty-bitmap: Change bdrv_[re]set_dirty_bitmap() to use bytes

dirty-bitmap: Change bdrv_[re]set_dirty_bitmap() to use bytes

Some of the callers were already scaling bytes to sectors; others
can be easily converted to pass byte offsets, all in our shift
towards a consistent byte interface everywhere.  Making the change
will also make it easier to write the hold-out callers to use byte
rather than sectors for their iterations; it also makes it easier
for a future dirty-bitmap patch to offload scaling over to the
internal hbitmap.  Although all callers happen to pass
sector-aligned values, make the internal scaling robust to any
sub-sector requests.

Signed-off-by: Eric Blake <[email protected]>
Reviewed-by: John Snow <[email protected]>
Reviewed-by: Kevin Wolf <[email protected]>
Reviewed-by: Fam Zheng <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>