block: Set request_alignment during .bdrv_refresh_limits()

block: Set request_alignment during .bdrv_refresh_limits()

We want to eventually stick request_alignment alongside other
BlockLimits, but first, we must ensure it is populated at the
same time as all other limits, rather than being a special case
that is set only when a block is first opened.

Add a .bdrv_refresh_limits() to all four of our legacy devices
that will always be sector-only (bochs, cloop, dmg, vvfat), in
spite of their recent conversion to expose a byte interface.

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