vfio/migration: Use BE byte order for device state wire packets

vfio/migration: Use BE byte order for device state wire packets

Wire data commonly use BE byte order (including in the existing migration
protocol), use it also for for VFIO device state packets.

This will allow VFIO multifd device state transfer between hosts with
different endianness.
Although currently there is no such use case, it's good to have it now
for completeness.

Reviewed-by: Avihai Horon <avihaih@nvidia.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Link: https://lore.kernel.org/qemu-devel/dcfc04cc1a50655650dbac8398e2742ada84ee39.1741611079.git.maciej.szmigiero@oracle.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>