Support for previous versions was
[removed](7194c847b6)
from geth in 2021 after other clients had migrated - should be safe to
remove here also.
* fix snappy detection - it should use the hello version, not the RLPx
handshake
* simplify generation of auth messages
* pad 100-300 bytes like spec suggests
TODO: error handling is all over the place - will be addressed in a
follow-up PR