cxgb3: assign port id to net_device->dev_port

T3 devices have different ports on same PCI function,
so using dev_port to identify ports.

Signed-off-by: Arjun Vynipadath <arjun@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>