…inter

This restores the EIP-8 test and the frame format test vector. In order
to make the latter test work, the code had to be restructured a bit,
permitting an optimization: message frames are no longer allocated twice
when decompressing. In ReadMsg, the compressed frame content was
previously put into a bytes.Reader, then slurped up into a fresh []byte
when decompressing.

Issue found by ineffassign

net.Pipe supports deadlines since Go 1.10.

It's useless now. Also return true size from Read to make metrics work.

This check is useless: the RLPx handshake works by encrypting the
initial packet to the destination key. The recipient cannot decrypt this
packet unless they have the matching private key.

For dialed connections, the RLPx implementation simply returns the
provided dial destination key as the remote identity, and we really
don't need to check it one more time after the handshake.