net: dsa: qca8k: limit user ports access to the first CPU port on setup

In preparation for multi-CPU support, set CPU port LOOKUP MEMBER outside
the port loop and setup the LOOKUP MEMBER mask for user ports only to
the first CPU port.

This is to handle flooding condition where every CPU port is set as
target and prevent packet duplication for unknown frames from user ports.

Secondary CPU port LOOKUP MEMBER mask will be setup later when
port_change_master will be implemented.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20230730074113.21889-3-ansuelsmth@gmail.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>