cxgb4: use dev_port to identify ports

Commit 3f85944f ("net: Add sysfs file
for port number") introduce dev_port to network devices. cxgb4 adapters
have multiple ports on the same PCI function, and used dev_id to
identify those ports. That use was removed by commit
8c367fcb ("cxgb4: Do not set
net_device::dev_id to VI index"), since dev_id should be used only when
devices share the same MAC address.

Using dev_port for cxgb4 allows different ports on the same PCI function
to be identified.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>