orangefs: clean up truncate ctime and mtime setting

The ctime and mtime are always updated on a successful ftruncate and
only updated on a successful truncate where the size changed.

We handle the ``if the size changed'' bit.

This matches FUSE's behavior.

Signed-off-by: Martin Brandenburg <martin@omnibond.com>
Signed-off-by: Mike Marshall <hubcap@omnibond.com>