Add definitions for PROBE ICMP types and codes.

Add AFI definitions for IP and IPV6 as specified by IANA

Add a struct to represent the additional header when probing by IP
address (ctype == 3) for use in parsing incoming PROBE messages

Add a struct to represent the entire Interface Identification Object
(IIO) section of an incoming PROBE packet
Signed-off-by: Andreas Roeseler <andreas.a.roeseler@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>