realtek: dsa: Drop LAG checks already handled by DSA handlers

realtek: dsa: Drop LAG checks already handled by DSA handlers

There is no need to check conditions in rtl83xx_lag_add()/rtl83xx_lag_del()
when they are already checked in
rtl83xx_port_lag_join()/rtl83xx_port_lag_leave().

Signed-off-by: Sven Eckelmann <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20707
Signed-off-by: Hauke Mehrtens <[email protected]>