databuf
    Points to a buffer that contains an extension header. This is a
    pointer returned by a call to inet6_opt_append().
 offset
    Specifies the location in the data portion of the option into
    which to insert the data. You can access the first byte after the
    option type and length by specifying the offset of 0 (zero).
 val
    Points to the data to be inserted.
 vallen
    Specifies the length of the data, in bytes, to be inserted.