Bluetooth: Fix double acking I-Frames when sending pending I-Frames

Pending I-Frame(s) are considered as acknowledgement. To void double
acking (via I-Frame and later via RR) clear ack timer when sending
first pending I-Frame.

Signed-off-by: Szymon Janc <szymon.janc@tieto.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

net/bluetooth/l2cap_core.c

@@ -1455,7 +1455,9 @@ static int l2cap_ertm_send(struct l2cap_chan *chan)
 
 		if (bt_cb(skb)->retries == 1) {
 			chan->unacked_frames++;
-			nsent++;
+
+			if (!nsent++)
+				__clear_ack_timer(chan);
 		}
 
 		chan->frames_sent++;