LU-532 llite: trusted. xattr is invisible to non-root

LU-532 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: Ic32fe262772370cd837bef878c9bfd9eefc0ec3c
Reviewed-on: http://review.whamcloud.com/2490
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>