mlx4_en: use net_device dev_id to indicate port number

Today, there are no means to know which port of a hardware device a netdev
interface uses. struct net_device conatins a field, dev_id, that can be used
for that. Use this field to save the port number in ConnectX that is being used
by the net device; port numbers are zero based.

Signed-off-by: Eli Cohen <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/mlx4/en_netdev.c

···
 	}
 
 	SET_NETDEV_DEV(dev, &mdev->dev->pdev->dev);
+	dev->dev_id =  port - 1;
 
 	/*
 	 * Initialize driver private data