Bluetooth: Stop ack_timer if ERTM enters in Local Busy or SREJ_SENT

The ack_timer is implemation specific, disabling it in such situation
avoids some potencial errors in the ERTM protocol.

Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Reviewed-by: João Paulo Rechi Vita <jprvita@profusion.mobi>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index c2fb26d..40cf67c1 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -3665,6 +3665,8 @@
 
 	pi->conn_state |= L2CAP_CONN_RNR_SENT;
 
+	del_timer(&pi->ack_timer);
+
 	queue_work(_busy_wq, &pi->busy_work);
 
 	return err;
@@ -3914,6 +3916,8 @@
 		pi->conn_state |= L2CAP_CONN_SEND_PBIT;
 
 		l2cap_send_srejframe(sk, tx_seq);
+
+		del_timer(&pi->ack_timer);
 	}
 	return 0;