vxlan_vni_in_use
if (vxlan_vni_in_use(src_net, old, conf, conf->vni)) {
int vxlan_vni_in_use(struct net *src_net, struct vxlan_dev *vxlan,
err = vxlan_vni_in_use(vxlan->net, vxlan, &vxlan->cfg, v);