Bluetooth: Check the tx_window size on setsockopt

We have to check if the proposed tx_window value is not greater that
maximum value supported.
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

@@ -1912,6 +1912,11 @@ static int l2cap_sock_setsockopt_old(struct socket *sock, int optname, char __us
 			break;
 		}
 
+		if (opts.txwin_size > L2CAP_DEFAULT_TX_WINDOW) {
+			err = -EINVAL;
+			break;
+		}
+
 		l2cap_pi(sk)->mode = opts.mode;
 		switch (l2cap_pi(sk)->mode) {
 		case L2CAP_MODE_BASIC: