mlxsw: spectrum: Support RED qdisc offload

Add support for ndo_setup_tc with enum tc_setup_type value of TC_SETUP_RED.
This call sets RED qdisc on a traffic class.
This patch supports RED qdisc only as a root qdisc and set in on the
default tclass. It can be set with or without ECN.

Signed-off-by: Yuval Mintz <yuvalm@mellanox.com>
Signed-off-by: Nogah Frankel <nogahf@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>