fix(dns): Dynamic DNS sorting so AF_UNSPEC works in IPv6-only network

This fix adds an option to dynamically set the order based on whether
an the host has a global (or ULA) IPv6 address, allowing a device
with both IPv4 and IPv6 enabled to work in any network configuration,
including IPv4-only, IPv6-only, and dual-stack.

Without the option there is a static ordering preferring IPv4, which
means on an IPv6-only network, a dual-stack destination returns the
IPv4 address, which fails. Setting the static preference to IPv6
would have the opposite problem. A dynamic sort, based on available
source addresses, is required to work on all networks.

Author: sgryphon