changes/ticket20895

   1   o Minor features (forward-compatibility):
   2     - If a relay supports some link authentication protocol that we do not
   3       recognize, then include that relay's ed25519 key when telling other
   4       relays to extend to it.  Previously, we treated future versions as if
   5       they were too old to support ed25519 link authentication.
   6       Closes ticket 20895.