mlxsw: spectrum: Support RED xstats

Add support for ndo_setup_tc with enum tc_setup_type value of
TC_SETUP_RED_XSTATS. This call returns the RED qdisc xstats from the cache
if the handle ID that is asked for matching the root qdisc ID and fails
otherwise.

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>