Currently it is possible to add e.g. an HTB Qdisc under ffff:fff1
(TC_H_INGRESS, TC_H_CLSACT):

  $ ip link add name ifb0 type ifb
  $ tc qdisc add dev ifb0 parent ffff:fff1 htb
  $ tc qdisc add dev ifb0 clsact
  Error: Exclusivity flag on, cannot modify.
  $ drgn
  ...
  >>> ifb0 = netdev_get_by_name(prog, "ifb0")
  >>> qdisc = ifb0.ingress_queue.qdisc_sleeping
  >>> print(qdisc.ops.id.string_().decode())
  htb
  >>> qdisc.flags.value_() # TCQ_F_INGRESS
  2

Only allow ingress and clsact Qdiscs under ffff:fff1.  Return -EINVAL
for everything else.  Make TCQ_F_INGRESS a static flag of ingress and
clsact Qdiscs.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Fixes: 1f211a1b ("net, sched: add clsact qdisc")
Tested-by: Pedro Tammela <pctammela@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>