mlxsw: spectrum: Collect tclass related stats periodically

Add more statistics to be collected from the HW periodically. These stats
are tclass based (beside ECN marked packet, that exist only port based).
They are needed to expose RED qdisc stats and xstats correctly.

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>