net: sched: don't take rtnl lock during flow_action setup

Refactor tc_setup_flow_action() function not to use rtnl lock and remove
'rtnl_held' argument that is no longer needed.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>