Add a rep cost to unexpected requests in statement distribution (peer rate limiting)

[Overkillus]

Issue postponed until most nodes update with the statement distribution rate limiting in #3444.

With the merge of #3444 we added peer limiting for statement distribution request response protocol. Nodes that already requested something from us should refrain from further requests until the first one finishes. For even better DoS prevention there could be a reputation punishment on the receiving side when encountering the unexpected request. While easy to do this was not added yet because older nodes are expected to continue sending those unexpected requests to newer nodes which might cause network fragmentation. Once a sufficient number of nodes update rep cost needs to be added which should fully close any relevant issues.