virtio_negotiate_features
features = virtio_negotiate_features(dev, VTBALLOON_FEATURES);
sc->vtblk_features = virtio_negotiate_features(dev, features);
sc->vtnet_features = virtio_negotiate_features(dev, features);
virtio_negotiate_features(dev, features);
sc->vtrnd_features = virtio_negotiate_features(dev, features);
features = virtio_negotiate_features(dev, VTSCSI_FEATURES);
uint64_t virtio_negotiate_features(device_t dev, uint64_t child_features);