This PR fixes two problems in devp2p tests (and through them, hive).

- Make the output more detailed about what is returned (always print packet kind).
- Allow Ping response to unsolicited findnode.

Without this PR, nethermind fails a hive protocol test, and I misinterpreted the result (NethermindEth/nethermind#3617). Ergo, the output was not fool-proof.