net: devlink: remove net namespace check from devlink_nl_port_fill()

It is ensured by the netdevice notifier event processing, that only
netdev pointers from the same net namespaces are filled. Remove the
net namespace check from devlink_nl_port_fill() as it is no longer
needed.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>