net: dsa: remove bool devlink_port_setup

Since dsa_port_devlink_setup() and dsa_port_devlink_teardown() are
already called from code paths which only execute once per port (due to
the existing bool dp->setup), keeping another dp->devlink_port_setup is
redundant, because we can already manage to balance the calls properly
(and not call teardown when setup was never called, or call setup twice,
or things like that).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>