[stable/dragonfish] ZIL block cloning fix & re-enable block cloning

[ixhamza]

1. To improve 128KB block write performance in case of multiple VDEVs ZIL used to spit those writes into two 64KB ones. Unfortunately it was found to cause LWB buffer overflow, trying to write maximum- sizes 128KB TX_CLONE_RANGE record with 1022 block pointers into 68KB buffer, since unlike TX_WRITE ZIL code can't split it. This is a minimally-invasive temporary block cloning fix until the following more invasive prediction code refactoring.
2. Re-enable Block cloning for dragonfish nightlies

Signed-off-by: Alexander Motin [email protected]
Sponsored by: iXsystems, Inc.

How Has This Been Tested?

• Build for dragonfish (in progress): https://ci.tn.ixsystems.net/jenkins/job/TrueNAS%20SCALE%20-%20Unstable/job/Build%20-%20TrueNAS%20SCALE_Custom/670/
• CI tests

Types of changes

• 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:

• 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.
• All commit messages are properly formatted and contain Signed-off-by.