Note:
Bitcoin ABC uses a different magic for network and disk messages. See D400 & D666. It makes more sense to use `DiskMagic` than to use `NetMagic` for disk data.
This is a backport of core#19077 [21/26]
https://github.com/bitcoin/bitcoin/pull/19077/commits/9d3d2d263c331e3c77b8f0d01ecc9fea0407dd17
Depends on D10568