IB/mlx5: Return PORT_ERR in Active to Initializing tranisition

FW port-change events are fired on Active <-> non Active port state
transitions only.
When the port state changes from Active to Initializing (Active ->
Down -> Initializing), a single event is fired.
The HCA transitions from Down to Initializing unless prevented from
doing so, hence the driver should also propagate events when the port
state is Initializing to consumers so they'll be aware that the port
is no longer Active and act accordingly.

Fixes: e126ba97

 ('mlx5: Add driver for Mellanox Connect-IB...')
Signed-off-by: Noa Osherovich <noaos@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>