net/mlx5: change device reference for secondary process

net/mlx5: change device reference for secondary process

rte_eth_devices[] is not shared between primary and secondary process, but
a static array to each process. The reverse pointer of device (priv->dev)
is invalid. Instead, priv has the pointer to shared data of the device,
  struct rte_eth_dev_data *dev_data;

Two macros are added,
  #define PORT_ID(priv) ((priv)->dev_data->port_id)
  #define ETH_DEV(priv) (&rte_eth_devices[PORT_ID(priv)])

Signed-off-by: Yongseok Koh <yskoh@mellanox.com>