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>
# Conflicts:
# p2p/rlpx/rlpx.go
# p2p/rlpx/rlpx_test.go
# p2p/server_test.go
