Bluetooth: l2cap: always unlock channel in l2cap_conless_channel()

Add missing call to 'l2cap_chan_unlock()' on receive error handling
path in 'l2cap_conless_channel()'.

Fixes: a24cce14 ("Bluetooth: Fix reference counting of global L2CAP channels")
Reported-by: syzbot+45ac74737e866894acb0@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=45ac74737e866894acb0Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

net/bluetooth/l2cap_core.c

@@ -6774,6 +6774,7 @@ static void l2cap_conless_channel(struct l2cap_conn *conn, __le16 psm,
 	bt_cb(skb)->l2cap.psm = psm;
 
 	if (!chan->ops->recv(chan, skb)) {
+		l2cap_chan_unlock(chan);
 		l2cap_chan_put(chan);
 		return;
 	}