ibmveth: Make array ibmveth_stats static

Fix sparse warning:
drivers/net/ethernet/ibm/ibmveth.c:96:21:
 warning: symbol 'ibmveth_stats' was not declared. Should it be static?

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>