LU-549 llite: Improve statfs performance if selinux is disabled

LU-549 llite: Improve statfs performance if selinux is disabled

Even if selinux is disabled, client still tries to get selinux
attributes from MDS. As xattrs are not yet cached, this significantly
slows down xattr heavy operations like ls -l. This patch forces
to return -EOPNOTSUPP on the client side if selinux is disabled.
It speeds up ls -l 25% for cold-cache case and 50% for hot-cache
case.

Signed-off-by: Yevheniy Demchenko <zheka@uvt.cz>
Signed-off-by: Keith Mannthey <keith@whamcloud.com>
Change-Id: I0c24bd8559818b0fae29a082790b392095f91ab5
:# Please enter the commit message for your changes. Lines starting
Reviewed-on: http://review.whamcloud.com/2904
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>