This change adds a test framework for the "eth" protocol and some basic tests. The tests can be run using the './devp2p rlpx eth-test' command.
This change moves the RLPx protocol implementation into a separate package, p2p/rlpx. The new package can be used to establish RLPx connections for protocol testing purposes. Co-authored-by: Felix Lange <fjl@twurst.com>