code: func ifaceAddIPv6Addr(iface *net.Interface, ip net.IP, mask net.IPMask) error {
  	prefixLen, _ := mask.Size()
  	return ipRunIface(iface, "addr add %s/%d dev %s", ip, prefixLen, iface.Name)
  }
docs: // ifaceAddIPv6Addr adds the given IPv6 address to the network interface.