Revert "net: dsa: Implement ndo_get_phys_port_id"

This reverts commit 3a543ef4 ("net: dsa:
Implement ndo_get_phys_port_id") since it misuses the purpose of
ndo_get_phys_port_id(). We have ndo_get_phys_port_name() to do the
correct thing for us now.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>