realtek: dsa: Adjust MSTP states after joining/leaving bridge

realtek: dsa: Adjust MSTP states after joining/leaving bridge

When joining a bridge or leaving a bridge, the CIST state will
automatically be adjusted by DSA using .port_stp_state_set(). But MSTIs are
completely unhandled.

If a port is joining a bridge, the default state must be disabled. The MSTP
daemon is then responsible for adjusting the state.

If the bridge is left, the forwarding state must be enforced because VLANs
(and with this also the MSTIs assigned to them) are shared between bridged
and non-bridged ports. An unbridged port must therefore not be left in an
blocked/disabled state for a VLAN (MSTI).

Suggested-by: Jonas Gorski <[email protected]>
Signed-off-by: Sven Eckelmann <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20421
Signed-off-by: Hauke Mehrtens <[email protected]>