Those options are not needed, because we need to only provide IPv6 address to
RU, and also they are not very meaningful: in the current form we tell RU that
DNS addresses sit at RU.addr+1 and RU.addr+2, i.e. in the IP range we give to
RU and also at the addresses where no DNS server is actually running.

It was probably a thinko to add those options initially.

/cc @jhuge, @xavier_thompson, @Daetalus
/reviewed-by @lu.xu
/reviewed-on nexedi/slapos!1472