(Only run the connection_or_group_set_badness_() function on groups
of channels that have the same RSA and Ed25519 identities.)

There's a possible opportunity here where we might want to set a
channel to "bad" if it has no ed25519 identity and some other
channel has some.  Also there's an opportunity to add a warning if
we ever have an Ed mismatch on open connections with the same RSA
ID.