* Handle the decodeAuthMessage error case separatly and log to trace
Garbage data on the TCP port (e.g. from port scanners) would
cause lots of error log messages, so log this to trace and get rid
of a (little) bit of exception usage in the process.
* Remove usage of result var in rlpxAccept and rlpxConnect
* Discv4: Add ENRRequest & ENRResponse msgs to avoid fails on these
Fix#499
These messages are not implemented yet however, but just ignored.