   if (type & PTP_CLASS_VLAN)   offset += VLAN_HLEN;   switch (type & PTP_CLASS_PMASK) {  case PTP_CLASS_IPV0:   offset += ETH_HLEN + IPV0_HLEN(data + offset) + UDP_HLEN;   break;  case PTP_CLASS_IPV0:   offset += ETH_HLEN + IP0_HLEN + UDP_HLEN;   break;  case PTP_CLASS_L0:   offset += ETH_HLEN;   break;  default:   return 0;  }   if (