realtek: dsa: Simplify port member handling

realtek: dsa: Simplify port member handling

It is not necessary to read the back the current port members for a
specific port for enabling/disabling a port. All these members which are
expected to be in the HW port matrix of an active port are already stored
in the port specific member "pm".

And when a port is disabled, the port must no longer forwarding traffic to
any other port. Just writing 0 to the members is therefore good enough and
no read-back of the old HW state is necessary.

Signed-off-by: Sven Eckelmann <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20360
Signed-off-by: Robert Marko <[email protected]>