LU-3484 llite: Anonymous dentry incorrectly identified as root

LU-3484 llite: Anonymous dentry incorrectly identified as root

When exporting Lustre via NFS on SLES11SP2, this check incorrectly identifies
anonymous dentries as root dentries.  This is due to a change in SLES11SP2
which makes the d_name.name for anonymous dentries the same as that for root
dentries.  (Details in LU-3484.)

This changes the check to directly compare the value of the dentry pointer
to the root dentry pointer found in the superblock, rather than using the name.

Signed-off-by: Patrick Farrell <paf@cray.com>
Change-Id: I18a60a7610b02d1b0580f9a0af4aeb81b5cca9b1
Reviewed-on: http://review.whamcloud.com/6726
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Peng Tao <bergwolf@gmail.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Alexey Shvetsov <alexxy@gentoo.org>