Revert "Temporarily disable Direct IO by default"

[behlendorf]

Motivation and Context

Re-enable direct IO by default now that the #16598 has been resolved.

Description

This reverts commit 4121059 now that b4e4cbe has been merged.

How Has This Been Tested?

This functional has been manually tested in #16598 and by all previous CI runs since it was integrated.

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.

[amotin]

There is still unresolved issue with potentially insufficient range locking in zfs_getpages() on FreeBSD.