6rd option added. DHCP_OPTIONS changed from record of to set of

Created by: semihalf-klimkowicz-jacek

DHCP_OPTIONS changed to 'set of' as DHCP client can set options on his own preferences. This also simplifies matching mechanism as i.e. superset can be used to verify the presence of specific options. This is non backward compatible change.

As DHCP client i am testing is configured to add 6rd option i included this definition (based on rfc 5969).

Signed-off-by: Jacek Klimkowicz jakl@semihalf.com