net: sched: Move to new offload indication in RED

Let RED utilize the new internal flag, TCQ_F_OFFLOADED,
to mark a given qdisc as offloaded instead of using a dedicated
indication.

Also, change internal logic into looking at said flag when possible.

Fixes: 602f3baf ("net_sch: red: Add offload ability to RED qdisc")
Signed-off-by: Yuval Mintz <yuvalm@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>