Bluetooth: Fix drop of packets with invalid req_seq/tx_seq

We shall not use an unsigned var since we are expecting negatives value
there. Using unsigned causes ERTM connection to close due to invalid
ReqSeq numbers.
Signed-off-by: NGustavo F. Padovan <padovan@profusion.mobi>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>

net/bluetooth/l2cap.c

@@ -3796,7 +3796,7 @@ static inline int l2cap_data_channel_iframe(struct sock *sk, u16 rx_control, str
 	u8 tx_seq = __get_txseq(rx_control);
 	u8 req_seq = __get_reqseq(rx_control);
 	u8 sar = rx_control >> L2CAP_CTRL_SAR_SHIFT;
-	u8 tx_seq_offset, expected_tx_seq_offset;
+	int tx_seq_offset, expected_tx_seq_offset;
 	int num_to_ack = (pi->tx_win/6) + 1;
 	int err = 0;
 
@@ -4081,7 +4081,8 @@ static inline int l2cap_data_channel(struct l2cap_conn *conn, u16 cid, struct sk
 	struct sock *sk;
 	struct l2cap_pinfo *pi;
 	u16 control, len;
-	u8 tx_seq, req_seq, next_tx_seq_offset, req_seq_offset;
+	u8 tx_seq, req_seq;
+	int next_tx_seq_offset, req_seq_offset;
 
 	sk = l2cap_get_chan_by_scid(&conn->chan_list, cid);
 	if (!sk) {