sunvnet: add stats to track ldom to ldom packets and bytes

In this driver, there is a "port" created for the connection to each of
the other ldoms; a netdev queue is mapped to each port, and they are
collected under a single netdev.  The generic netdev statistics show
us all the traffic in and out of our network device, but don't show
individual queue/port stats.  This patch breaks out the traffic counts
for the individual ports and gives us a little view into the state of
those connections.

Orabug: 25190537

Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>