vdpa: fix network breakage after cancelling migration

vdpa: fix network breakage after cancelling migration

Fix an issue where cancellation of ongoing migration ends up
with no network connectivity.

When canceling migration, SVQ will be switched back to the
passthrough mode, but the right call fd is not programed to
the device and the svq's own call fd is still used. At the
point of this transitioning period, the shadow_vqs_enabled
hadn't been set back to false yet, causing the installation
of call fd inadvertently bypassed.

Message-Id: <1707910082-10243-13-git-send-email-si-wei.liu@oracle.com>
Fixes: a8ac88585da1 ("vhost: Add Shadow VirtQueue call forwarding capabilities")
Cc: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>