bpf: net_sched: Support implementation of Qdisc_ops in bpf

The recent advancement in bpf such as allocated objects, bpf list and bpf
rbtree has provided powerful and flexible building blocks to realize
sophisticated packet scheduling algorithms. As struct_ops now supports
core operators in Qdisc_ops, start allowing qdisc to be implemented using
bpf struct_ops with this patch. Users can implement Qdisc_ops.{enqueue,
dequeue, init, reset, destroy} in bpf and register the qdisc dynamically
into the kernel.

Co-developed-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Amery Hung <amery.hung@bytedance.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://patch.msgid.link/20250409214606.2000194-3-ameryhung@gmail.com