Restore atapi_dma flag across migration

Restore atapi_dma flag across migration

If a migration happens just after the guest has kicked
off an ATAPI command and kicked off DMA, we lose the atapi_dma
flag, and the destination tries to complete the command as PIO
rather than DMA.  This upsets Linux; modern libata based kernels
stumble and recover OK, older kernels end up passing bad data
to userspace.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>