pNFS: Allow layout drivers to manage private data in struct nfs4_layoutreturn

Cleanup to allow layout drivers to attach private data to layoutreturn,
and manage the data.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
index 84fdcf2..1c1768a 100644
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -2035,7 +2035,9 @@
 	spin_lock(&args->inode->i_lock);
 	encode_nfs4_stateid(xdr, &args->stateid);
 	spin_unlock(&args->inode->i_lock);
-	if (lr_ops->encode_layoutreturn)
+	if (args->ld_private->ops && args->ld_private->ops->encode)
+		args->ld_private->ops->encode(xdr, args, args->ld_private);
+	else if (lr_ops->encode_layoutreturn)
 		lr_ops->encode_layoutreturn(xdr, args);
 	else
 		encode_uint32(xdr, 0);