cxgb4vf: configure ports accessible by the VF

Find ports accessible by the VF, based on the index of the
mac address stored for the VF in the adapter. If no mac address
is stored for the VF, use the port mask provided by firmware.

Signed-off-by: Nirranjan Kirubaharan <nirranjan@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>