dhcpv6: always include IA_NA and IA_PD in Request message if requested

dhcpv6: always include IA_NA and IA_PD in Request message if requested

RFC7550 says that if you request both IA_NA and IA_PD and only one
option is offered in the Advertise, then the client must send a Request
message (and not a Solicit) and the message SHOULD still include both
IA_NA and IA_PD options.

Problem: A Request message is correctly sent instead of a Solicit but it
doesn't include both IA_NA and IA_PD options.

Solution: If IA_NA and IA_PD are requested, the Request message always
includes both options.

Signed-off-by: Nicolas BESNARD <[email protected]>
Signed-off-by: Paul Donald <[email protected]>
Link: https://github.com/openwrt/odhcp6c/pull/106
Signed-off-by: Álvaro Fernández Rojas <[email protected]>