LU-1113 llite: hide DCACHE_LUSTRE_INVALID in ll_dentry_data

LU-1113 llite: hide DCACHE_LUSTRE_INVALID in ll_dentry_data

DCACHE_LUSTRE_INVALID is lustre private flag in vfs layer.
Replace it with dentry->d_fsdata->lld_invalid so that it won't
conflict with VFS flags.

After dcache scalability patch, dentry->d_fsdata is always set
before dentry is materised/rehashed. So if a dentry's d_fsdata
is not set, then it is not hashed/materised. The patch make use
of the fact and treat such dentry as invalid as well. It is
necessary because d_lustre_invalidate() can be called in
ll_invalidate_negative_children() and finds unmaterised/unhashed
dentries.

Also drop all vfs_races patches as they are no longer needed.

Plus two minor cleanups.

Signed-off-by: Peng Tao <tao.peng@emc.com>
Change-Id: I655154b8807440c99574ad6b865bd550cbc145f1
Reviewed-on: http://review.whamcloud.com/2407
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Reviewed-by: Lai Siyao <laisiyao@whamcloud.com>