batman-adv: tp_meter: initialize dec_cwnd explicitly

When batadv_tp_update_cwnd() is called, dec_cwnd is increased. But dec_cwnd
is only initialixed (to 0) when a duplicate Ack was received or when cwnd
is below the ss_threshold.

Just initialize the cwnd during the initialization to avoid any potential
access of uninitialized data.

Cc: stable@kernel.org
Fixes: 33a3bb4a33 ("batman-adv: throughput meter implementation")
Signed-off-by: Sven Eckelmann <sven@narfation.org>

net/batman-adv/tp_meter.c

@@ -1055,6 +1055,8 @@ void batadv_tp_start(struct batadv_priv *bat_priv, const u8 *dst,
 	 * mesh_interface, hence its MTU
 	 */
 	tp_vars->cwnd = BATADV_TP_PLEN * 3;
+	tp_vars->dec_cwnd = 0;
+
 	/* at the beginning initialise the SS threshold to the biggest possible
 	 * window size, hence the AWND size
 	 */