Added fsync on/off support.

Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>
fs: sync: enable fsync by default.

Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>
fs: sync: add missing return if fsync is disabled from userspace.

Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>