mlxsw: spectrum: qdiscs: Add tclass number to the mlxsw_sp_qdisc

Tclass number is needed for most of the operations related to the qdisc in
the driver. Create a field for it in the mlxsw_sp_qdisc instead of passing
it to every function as parameter.

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