As discussed in https://github.com/bitcoin/bitcoin/issues/19943, this
test may be a bit misleading to newcomers.
We underscore the fact that our peer needs to run a modified version of
Bitcoin Core to actually relay transactions to a `blocksonly` node and
benefit from the `whitelistforcerelay` parameter.
If we set fRelay=false in our VERSION message, and a peer sends an INV or TX
message anyway, disconnect. Since we use fRelay=false to minimize bandwidth,
we should not tolerate remaining connected to a peer violating the protocol.