cxgb4: Set mac addr from vpd, when we can't contact firmware

Grab the Adapter MAC Address out of the VPD and use it for the "debug"
network interface when either we can't contact the firmware

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>