fac3a054cb test: Fix race in p2p_invalid_messages (MarcoFalke)
Pull request description:
After we change our magic bytes, the node may or may not send us messages such as feefilter or sendheaders, which would be rejected by `_on_data`.
Solve that by replacing `_on_data` with a noop.
Tree-SHA512: bd25a81f0c6e31f09155e00abab8062777d827b9210d6a9b85ef35cfe5069338f100fecf058842f41a1f134fdb3cf7ac1fe80db493e4dab7988acdacb33149df
Backport of Core PR15330