vhost-user: send log shm fd along with log_base Send the shm for the dirty pages logging if the backend supports VHOST_USER_PROTOCOL_F_LOG_SHMFD. Wait for a reply to make sure the old log is no longer used. Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Tested-by: Thibaut Collet <thibaut.collet@6wind.com>