[6.0]sched: fix an oops when dump the qdisc of loopback device

Issue

• The loopback device use noqueue_qdisc for qdisc, and the noqueue_qdisc's dev_queue is  noqueue_netdev_queue, but the noqueue_netdev_queue.dev is NULL.

• When dumping the loopback device's qdisc use netlink with nlmsg_type=RTM_GETQDISC, nlmsg_flags=NLM_F_REQUEST, and tcmsg.tcm_parent = TC_H_ROOT, it will call the function tc_fill_qdisc() to get the qdisc, but in function tc_fill_qdisc(), the qdisc_dev(q)->ifindex will reference an null pointer, and causes the OOPS.

   int main(int argc, char *argv[])
   {
        struct {
                struct nlmsghdr nlmsg;
                struct tcmsg tcmsg;
        } msg;
        ...
        fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
        ...
        msg.nlmsg.nlmsg_type = RTM_GETQDISC;
        msg.nlmsg.nlmsg_flags = NLM_F_REQUESTM_F_ACK;
        msg.tcmsg.tcm_parent = TC_H_ROOT;
        send(fd, &msg, sizeof msg, 0);
        ...
   }