Bluetooth: Simplify the ERTM ack timeout

Since l2cap_send_ack can trigger extra actions like sending iframes,
don't call it.  Just send an RR or RNR frame if an ack needs sending.
Signed-off-by: Mat Martineau <mathewm@codeaurora.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

net/bluetooth/l2cap_core.c

@@ -2762,15 +2762,19 @@ static void l2cap_ack_timeout(struct work_struct *work)
 {
 	struct l2cap_chan *chan = container_of(work, struct l2cap_chan,
 					       ack_timer.work);
+	u16 frames_to_ack;
 
 	BT_DBG("chan %p", chan);
 
 	l2cap_chan_lock(chan);
 
-	l2cap_send_ack(chan);
+	frames_to_ack = __seq_offset(chan, chan->buffer_seq,
+				     chan->last_acked_seq);
 
-	l2cap_chan_unlock(chan);
+	if (frames_to_ack)
+		l2cap_send_rr_or_rnr(chan, 0);
 
+	l2cap_chan_unlock(chan);
 	l2cap_chan_put(chan);
 }