core: change the priority order in static "ipv6.addresses"

The order of addresses matters. For "ipv4.addresses", the list
contains the primary address first. For "ipv6.addresses", the
order was reverted. This was also documented behavior.

The previous patch just changed behavior with respect to relative order
of static IPv6 addresses and autoconf6/DHCPv6. As we seem in the mood
for changing behavior, here is another one.

Now the addresses are interpreted in an order consistent with IPv4 and
how one might expect: preferred addresses first.
57 jobs for th/ipv6-address-order-rh2073032 in 31 minutes and 12 seconds (queued for 10 seconds)