NFS: Create nfs_open_dir_context

nfs_opendir() created a context that held much more information than we
need for a readdir.  This patch introduces a slimmed-down
nfs_open_dir_context that contains only the cookie and the cred used for
RPC operations.  The new context will eventually be used to help detect
readdir loops.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index cb2add4..4b851a0 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -95,7 +95,10 @@
 	int error;
 
 	struct list_head list;
+};
 
+struct nfs_open_dir_context {
+	struct rpc_cred *cred;
 	__u64 dir_cookie;
 };