Fix for AIX machines with IPv6 disabled.

[apenney]

This attempts to handle the fact that NTP seems to explode if IPv6
is disabled on AIX, ntp becomes unable to parse the -6 lines that
we rely on in $restrict. It also apparently predates the KoD filtering
capabilities. As this stands for 'Kiss of Death' we certainly want to
retain this filtering capability for other distributions and operating
systems.

[puppetlabs-jenkins]

🔴 Test failed.
Refer to this link for build results: http://jenkins-modules.delivery.puppetlabs.net/job/puppetlabs-grizzly%20pull%20requests/9/

[hunner]

What happens on AIX when there is IPv6? Should this PR target the supported branch?

[hunner]

Why is puppetlabs-grizzly commenting here?

[hunner]

Also, if someone wants to override the default restrict lines, they just have to pass restrict to the base class. AIX without IPv6 could always do that. (Not as good as detecting IPv6, but still a plausible workaround)

[apenney]

The current situation with this would be AIX users would have to pass their own IPv6 stuff in. $ipaddress6 isn't supported in AIX so we have no way to autodetermine if it's enabled, and only AIX fails if it's disabled (as far as I'm aware).
Either way AIX fails with the kod line on ipv4 and ipv6 and we want that on all other distributions. I would feel weird about having a special README thing that says AIX users have to pass custom restrict lines, but that's a totally valid potential workaround. Supported modules doesn't imply "always works with the defaults", I don't think.

[apenney]

Also I never like targeting older branches and merging up, it just feels so wrong to me, that's why I always target master and backport to 3.0.x branches. I can't shake it, it feels horribly wrong to target anything but master with stuff I want to carry forward..