nlmclnt_unlock_prepare
if (nlmclnt_ops && nlmclnt_ops->nlmclnt_unlock_prepare)
defer_call = nlmclnt_ops->nlmclnt_unlock_prepare(task, req->a_callback_data);
.rpc_call_prepare = nlmclnt_unlock_prepare,
.nlmclnt_unlock_prepare = nfs3_nlm_unlock_prepare,
bool (*nlmclnt_unlock_prepare)(struct rpc_task*, void *);