Bluetooth: Fix bug with ERTM vars increment

All ERTM operations regarding the txWindow should be modulo 64,
otherwise we confuse the ERTM logic and connections will break.
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>

net/bluetooth/l2cap.c

@@ -3748,7 +3748,7 @@ static void l2cap_check_srej_gap(struct sock *sk, u8 tx_seq)
 		l2cap_ertm_reassembly_sdu(sk, skb, control);
 		l2cap_pi(sk)->buffer_seq_srej =
 			(l2cap_pi(sk)->buffer_seq_srej + 1) % 64;
-		tx_seq++;
+		tx_seq = (tx_seq + 1) % 64;
 	}
 }
 
@@ -3784,10 +3784,11 @@ static void l2cap_send_srejframe(struct sock *sk, u8 tx_seq)
 		l2cap_send_sframe(pi, control);
 
 		new = kzalloc(sizeof(struct srej_list), GFP_ATOMIC);
-		new->tx_seq = pi->expected_tx_seq++;
+		new->tx_seq = pi->expected_tx_seq;
+		pi->expected_tx_seq = (pi->expected_tx_seq + 1) % 64;
 		list_add_tail(&new->list, SREJ_LIST(sk));
 	}
-	pi->expected_tx_seq++;
+	pi->expected_tx_seq = (pi->expected_tx_seq + 1) % 64;
 }
 
 static inline int l2cap_data_channel_iframe(struct sock *sk, u16 rx_control, struct sk_buff *skb)