During last week's IRC meeting, we ran into a question about validating
the configuration options for ipv6_address_mode[1] and ipv6_ra_mode[1] for
IPv6 networks. This brought up a few issues, but after mulling it over for
a while I think it breaks down into 2 distinct questions.
Question 1)
For Question 1, I think we can allow potential use cases (even OpenStack
doesn't support it for now), but we should not permit the combinations of
modes which don't make any sense.
For Question 2, for modes which don't make sense, I think error messages
and return code are needed. For mode
