ip6_flow
header->ip6_flow = htonl(flowinfo) & IPV6_FLOWINFO_MASK;
uint8 ServiceType() const { return ntohl(header.ip6_flow) >> 20;}
u_int32_t flow = ip6->ip6_flow & IPV6_FLOWLABEL_MASK;
offsetof(struct ip6_hdr, ip6_flow), sizeof(flow),
flowlabel = ntohl(ip6.ip6_flow);