o Minor feature (IPv6):
    - When a consensus has IPv6 ORPorts, make IPv6-only clients use them,
      rather than waiting to download microdescriptors.
      Implements 23827.
    - Make IPv6-only clients wait for microdescs for relays, even if we were
      previously using descriptors (or were using them as a bridge) and have
      a cached descriptor for them.
      Implements 23827.