NFS: Create a free_client rpc_op

NFS v4 needs a way to shut down callbacks and sessions, but v2 and v3
don't.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 035f7a0..f301c53 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -6807,6 +6807,7 @@
 	.have_delegation = nfs4_have_delegation,
 	.return_delegation = nfs4_inode_return_delegation,
 	.init_client	= nfs4_init_client,
+	.free_client	= nfs4_free_client,
 };
 
 static const struct xattr_handler nfs4_xattr_nfs4_acl_handler = {