LU-911 defs: XATTR_NAME_FID defition

LU-911 defs: XATTR_NAME_FID defition

to be used by OFD later to store back pointer
to MDS object referencing this OST object.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I5c7b4838efa9064eedf6c530d9eb54bed9e602fb
Signed-off-by: Mikhail Pershin <tappro@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1839
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>