LU-1838 llite: trusted. xattr is invisible to non-root

LU-1838 llite: trusted. xattr is invisible to non-root

Filter out all invalid xattrs in listxattr.
This includes trusted. xattrs that can cause
unnecessary "EPERM" in subsequent getxattr operations.

Signed-off-by: Fan Yong <yong.fan@whamcloud.com>
Signed-off-by: Bob Glossman <bogl@whamcloud.com>
Change-Id: I9613444adcdb14067a775f68f951af7a9b941e9a
Reviewed-on: http://review.whamcloud.com/3892
Tested-by: Hudson
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>