net: devlink: add warning for ndo_get_port_parent_id set when not needed

Currently if the driver registers devlink port instance, he should set
the devlink port attributes as well. Then the devlink core is able to
obtain switch id itself, no need for driver to implement the ndo.
Once all drivers will implement devlink port registration, this ndo
should be removed. This warning guides new drivers to do things as
they should be done.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>