NFSv4.1: Don't process the sequence op more than once.

Ensure that if we call nfs41_sequence_process() a second time for the
same rpc_task, then we only process the results once.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfs4proc.c

@@ -754,7 +754,7 @@ static int nfs41_sequence_process(struct rpc_task *task,
 	if (slot == NULL)
 		goto out_noaction;
 	/* don't increment the sequence number if the task wasn't sent */
-	if (!RPC_WAS_SENT(task))
+	if (!RPC_WAS_SENT(task) || slot->seq_done)
 		goto out;
 
 	session = slot->table->session;