net: ibmveth: Remove unused stats member from struct ibmveth_adapter

The ibmveth driver keeps its statistics in net_device->stats, so the
stats member in struct ibmveth_adapter is unused. Remove it.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>