extbuf
    Points to a buffer that contains an extension header.
 extlen
    Specifies the length, in bytes, of the extension header.
 offset
    Specifies the location in the extension header of an option.
    Valid values are either 0 (zero) for the first option or the
    length returned from a previous call to either inet6_opt_next()
    or inet6_opt_find().
 type
    Specifies the type of option to find.
 lenp
    Points to the length of the option found.
 databufp
    Points to the option data.