zfs_debug: Restore log size limit for userspace

[amotin]

For some reason it was dropped when split from kernel, that made raidz_test to accumulate in RAM up to 100GB of logs we don't need.

Fixes #16492 Fixes #16566

How Has This Been Tested?

Manually run ./raidz_test -S -e -t 300 and observed its memory usage.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Performance enhancement (non-breaking change which improves efficiency)
• [ ] Code cleanup (non-breaking change which makes code smaller or more readable)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• [ ] Documentation (a change to man pages or other documentation)

Checklist:

• [x] My code follows the OpenZFS code style requirements.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the contributing document.
• [ ] I have added tests to cover my changes.
• [ ] I have run the ZFS Test Suite with this change applied.
• [x] All commit messages are properly formatted and contain Signed-off-by.

[robn]

Ugh, yeah, fair enough. I don't think I removed this on purpose, more likely just didn't obviously see anything that needed it. Thanks!