LU-139 move DCACHE_LUSTRE_INVALID to higher bit to prevent conflict with other dentry...

LU-139 move DCACHE_LUSTRE_INVALID to higher bit to prevent conflict with other dentry flags

2.6.38 comes with a bunch of new dentry flags and one of them
(i.e. DCACHE_OP_REVALIDATE) conflicts with our DCACHE_LUSTRE_INVALID.

Change-Id: I11de689058d12b07b2f00191f2d175d48a90ff8e
Signed-off-by: Johann Lombardi <johann@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/339
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>