rocker: use change upper info

Since now information about changed upper is passed along, benefit from
that and use this info directly.

This also fixes possible issues that could happen when non-master device
is added (current code does not distinguish between master and non-master
upper device).

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