Include both declared and reachable IPv6 OR addresses

When a relay declares an IPv6 OR address, it puts it in its descriptor, and it gets placed in the microdescriptor automatically.

But the IPv6 addresses in the full consensus are different: authorities on IPv6 only vote for an IPv6 address if they believe it is reachable.

(There are no IPv6 addresses in the microdesc consensus, see legacy/trac#20916 (moved).)

This makes a difference on Atlas tickets like legacy/trac#10401 (moved).

(It doesn't make a difference to client behaviour yet, because microdescs are the default. We'll fix that in legacy/trac#20916 (moved).)