The old implementation of the 'stable' flag to the resolve_ipnets()
function just sorted the addresses for each host based on their
textual representation, without regard for which address family they
belonged to.  That meant that 192.0.2.17 would always come before
2001:db8:17:23::99, which would always come before 203.0.113.23.  That
is probably not the best behaviour, since you sometimes want to prefer
one address family over the other.

We improve on this by coalescing and grouping addresses by address
family, and only sort the addresses within each family.  This may
still break the Default Address Selection order (RFC 3484/6724)
implemented by the getaddrinfo(3) function, but it is at least better
than before.

We now also obey the order that the 'ipv4' and 'ipv6' flags are given
in; if 'ipv6' is specified before 'ipv4', IPv6 addresses will be
returned before IPv4 addresses, and vice versa.  Also, if no address
family is specified, we now pass AF_UNSPEC to getaddrinfo() instead of
querying for IPv4 addresses and IPv6 addresses separately in whatever
order they were stored in the RESOLVE_IPNETS__IPFAMILIES hash.  Thus,
we will then obey the ordering returned by getaddrinfo() a little bit
better.  (But remember that resolve_ipnets() is evaluated on the
Puppet master, not on the node being configured, so the order may
still not be what is wanted.)

This was originally commit 4d5b4bfe3462 in nsc-puppet-utils.