the full length from offset is being flushed. Note that for now VOP_FSYNC
does not support offset and length parameters so we still do the same full
VOP_FSYNC. This issue was reported at FreeNAS support site as FreeNAS
ticket #1096.
Submitted by: "ceckerle" <ce.freenas eckerle net>
Prodded by: gcooper
Reviewed by: rmacklem
MFC after: 2 weeks