Instead of patching BlockHeader or BlockBody codec
each time it get additional optional fields,
this PR make the rlp codec automatically handle
optional fields. Thus rlp codec overloading of
EthBlock, BlockHeader, and BlockBody can be removed.
For a long time this caused invalid RLP parsing of `NewBlock` messages in the
`eth` protocol.
The `rlpInline` pragma was accepted but had no effect. We could implemented
it, but it doesn't seem worth doing, with tests etc, as there's only one user
which has been fixed another way.
With `NewBlock`, whenever a peer sent us `NewBlock`, we'd get an RLP decoding
error, and disconnected the peer thinking it was the peer's error.
These messages are sent often by good peers, so whenever we connected to a
really good peer, we'd end up disconnecting within a minute due to this. This
went unnoticed for years, as we stayed connected to old peers which have no new
blocks, and we weren't looking at peer quality, disconnect reasons or real-time
blockchain updates anyway.
Signed-off-by: Jamie Lokier <jamie@shareable.org>