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 for the first option or the length
    returned from a previous call to either inet6_opt_next() or
    inet6_opt_find().
 typep
    Points to the type of the option found.
 lenp
    Points to the length of the option found.
 databufp
    Points to the option data.