commit f0c63124 upstream.

This fixes a failure in xfstests generic/313 because nfs doesn't update
mtime on a truncate.  The protocol requires this to be done implicity
for a size changing setattr.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>