After changing the parent_id to be the same for both NICs of same
the hardware device, netdev_port_same_parent_id now returns true for
more cases (all the lower devices in the hierarchy are on the same
hardware device).

If merged eswitch isn't enabled, these cases aren't supported, so disallow
them.
Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>