Address learning should initially be turned off by the driver for port
operation in standalone mode, then the DSA core handles changes to it
via ds->ops->port_bridge_flags().

Currently this is not the case for qca8k where learning is enabled
unconditionally in qca8k_setup for every user port.

Handle ports configured in standalone mode by making the learning
configurable and not enabling it by default.

Implement .port_pre_bridge_flags and .port_bridge_flags dsa ops to
enable learning for bridge that request it and tweak
.port_stp_state_set to correctly disable learning when port is
configured in standalone mode.
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/20230730074113.21889-2-ansuelsmth@gmail.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>