pnfs: save layoutcommit cred at layout header init

No need to save it for every lseg.
No need to save it at every pnfs_set_layoutcommit.

[Needed in v3.0]
CC: Stable Tree <stable@kernel.org>
Signed-off-by: Peng Tao <peng_tao@emc.com>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Jim Rees <rees@umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/pnfs.h

diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index 1eb2c04..1f5cb47 100644
--- a/fs/nfs/pnfs.h
+++ b/fs/nfs/pnfs.h
@@ -44,7 +44,6 @@
 	atomic_t pls_refcount;
 	unsigned long pls_flags;
 	struct pnfs_layout_hdr *pls_layout;
-	struct rpc_cred	*pls_lc_cred; /* LAYOUTCOMMIT credential */
 };
 
 enum pnfs_try_status {
@@ -125,6 +124,7 @@
 	u32			plh_barrier; /* ignore lower seqids */
 	unsigned long		plh_flags;
 	loff_t			plh_lwb; /* last write byte for layoutcommit */
+	struct rpc_cred		*plh_lc_cred; /* layoutcommit cred */
 	struct inode		*plh_inode;
 };