LU-932 llite: cleanup ll_inode_info to reduce inode size

LU-932 llite: cleanup ll_inode_info to reduce inode size

ll_inode_info contains many special-used members, some of them are only
used for directory object, some are only used for non-directory object.
Share memory between those non-coexist members to reduce inode size.

Signed-off-by: Fan Yong <yong.fan@whamcloud.com>
Change-Id: Ic10014b2121f64718667addb77ed009aa29c1b4c
Reviewed-on: http://review.whamcloud.com/1691
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Bobi Jam <bobijam@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>