net: dsa: vsc73xx: start treating the BR_LEARNING flag

This patch implements .port_pre_bridge_flags() and .port_bridge_flags(),
which are required for properly treating the BR_LEARNING flag. Also,
.port_stp_state_set() is tweaked and now disables learning for standalone
ports.

Disabling learning for standalone ports is required to avoid situations
where one port sees traffic originating from another, which could cause
packet drops.

Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://patch.msgid.link/20240713211620.1125910-13-paweldembicki@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>