ip6_vfc
header->ip6_vfc |= IPV6_VERSION;
uint8 ProtocolVersion() const { return header.ip6_vfc & IPV6_VERSION_MASK; }
tc = *(&ip6->ip6_vfc + 1); /* XXX */
tc |= (ip6->ip6_vfc << 4);
(ip6->ip6_vfc & IPV6_VERSION_MASK) >> 4, tc, (u_int32_t)ntohl(flow),