fix r324011, MFV of r323535, 8585 improve batching done in zil_commit()

I managed to commit an older version of the change.
Plus, even the latest version was not ready for userland compilation.

Reported by: "O. Hartmann" <ohartmann@walstatt.org>,

		cy

MFC after: 1 week
X-MFC with: r324011