Merge #15330: test: Fix race in p2p_invalid_messages

Summary:
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

Test Plan: test_runner.py p2p_invalid_messages

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D6395