NFSv4: Convert nfs41_free_stateid to use an asynchronous RPC call

The main reason for doing this is will be to allow for an asynchronous
RPC mode that we can use for freeing lock stateids as per section
8.2.4 of RFC5661.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index 766c5bc..104b62f 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -1176,7 +1176,7 @@
 
 struct nfs41_free_stateid_args {
 	struct nfs4_sequence_args	seq_args;
-	nfs4_stateid			*stateid;
+	nfs4_stateid			stateid;
 };
 
 struct nfs41_free_stateid_res {