As specified in RFC6106, DNSSL option contains one or more domain names
of DNS suffixes.  8-bit identifier of the DNSSL option type as assigned
by the IANA is 31.  This option should also be treated as userland.
Signed-off-by: NAlexey I. Froloff <raorn@raorn.name>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>