The macro IP6_HDR builds an IPv6 header, as defined in
[RFC2460]. The macro IP6_PCK is synonymous to
IP6_HDR, except that it also sets the protocol to
ETH_P_IPV6 with ``default'' priority.
Note that $ip6_src and $ip6_dst are of type ``IPv6 address''.
$ip6_dst = ::18.104.22.168 send IP6_PCK($ip6_tc=0xe0 $ip6_nxt=46) /* pretend this is RSVP */