net: sched: Support specifying a starting chain via tc skb ext

Set the starting chain from the tc skb ext chain value. Once we read
the tc skb ext, delete it, so cloned/redirect packets won't inherit it.

In order to lookup a chain by the chain index on the ingress block
at ingress classification, provide a lookup function.

Co-developed-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>