Connecting node with old pubkey

[Elfoniok]

There is a problem when connecting to node who's public key (so enode address also) changed.

If node change its address, it will be still addressed by others with its old address, but since it doesn't use old one it is impossible to decode messages sent to him and thus results in errors.

Previously it was asserts, now there are mostly format errors:
9cd6fbf

So right now it's handled but its hard to know what is happening, actual error was just hidden under the carpet. There could be some kind of logic when someone is trying to sent you messages using old enode address to simply notify the user.

There is also possibility of improvements? For example maybe nodes should broadcast whenever its enode address will change?