NFS: Create a return_delegation rpc op

Delegations are a v4 feature, so push return_delegation out of the
generic client by creating a new rpc_op and renaming the old function to
be in the nfs v4 "namespace"

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/unlink.c b/fs/nfs/unlink.c
index 3210a03..13cea63 100644
--- a/fs/nfs/unlink.c
+++ b/fs/nfs/unlink.c
@@ -501,7 +501,7 @@
 		(unsigned long long)NFS_FILEID(dentry->d_inode));
 
 	/* Return delegation in anticipation of the rename */
-	nfs_inode_return_delegation(dentry->d_inode);
+	NFS_PROTO(dentry->d_inode)->return_delegation(dentry->d_inode);
 
 	sdentry = NULL;
 	do {