This uses the same timeout as the getattr cache. This substantially
increases performance when writing files with smaller buffer sizes.
When writing, the size is (often) changed, which causes a call to
notify_change which calls security_inode_need_killpriv which needs a
getxattr. Caching it reduces traffic to the server.
Signed-off-by: Martin Brandenburg <martin@omnibond.com> Signed-off-by: Mike Marshall <hubcap@omnibond.com>