[MIR] ndisc6

Availability: In universe for all architectures.

Rationale: This package helps meet the goals in https://blueprints.launchpad.net/ubuntu/+spec/foundations-o-ipv6-healthcheck. Specifically, rdnssd-udeb is used by the netcfg ipv6 branch to discover DNS servers on IPv6 networks, and ndisc6-udeb is used by the netcfg ipv6 branch to analyse what kind of configuration (SLAAC only, stateless DHCPv6, or stateful DHCPv6) is required on a network based on its router advertisements.

Security: ndisc6 ships three setuid-root binaries: rdisc6, ndisc6, and rltraceroute6, for the usual SOCK_RAW kinds of reasons; and rdnssd ships a daemon by the same name. I don't see any history of security vulnerabilities, but I expect it will need a security review due to the setuid binaries anyway. To my eye the code seems pretty clear (it's basically just packet-banging code), and it has the virtue of being small; however, I have only scanned it fairly briefly.

QA: Mostly tools with little configuration required. No bug reports of great concern in Debian or Ubuntu. No test suite as far as I can see. Includes a watch file.

UI standards: N/A.

Dependencies: The udebs are all I need at this time, and their dependencies are straightforward and already in main. The rdnssd deb recommends resolvconf, which we'd probably want to drop to a suggests if we promoted the deb to main as well, but we would notice that at the time of promotion.

Standards compliance: Straightforward-looking CDBS packaging; seems to meet the relevant standards for both debs and udebs.

Maintenance: I expect we can just keep this synced from Debian. The foundations team will deal with issues that specifically affect the foundations-o-ipv6-healthcheck specification, but in my testing so far I haven't run across any.