batman-adv: tp_meter: fix fast recovery precondition

commit 2b0d08f upstream.

The fast recovery precondition checks if the recover (initialized to
BATADV_TP_FIRST_SEQ) is bigger than the received ack. But since recover is
only updated when this check is successful, it will never enter the fast
recovery mode.

According to RFC6582 Section 3.2 step 2, the check should actually be
different:

> When the third duplicate ACK is received, the TCP sender first
> checks the value of recover to see if the Cumulative
> Acknowledgment field covers more than recover

The precondition must therefore check if recover is smaller than the
received ack - basically swapping the operands of the current check.

Cc: stable@kernel.org
Fixes: 33a3bb4 ("batman-adv: throughput meter implementation")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: ecsv

net/batman-adv/tp_meter.c

@@ -733,7 +733,7 @@ static void batadv_tp_recv_ack(struct batadv_priv *bat_priv,
 		if (atomic_read(&tp_vars->dup_acks) != 3)
 			goto out;
 
-		if (recv_ack >= tp_vars->recover)
+		if (tp_vars->recover >= recv_ack)
 			goto out;
 
 		/* if this is the third duplicate ACK do Fast Retransmit */