net: get stats64 if device if driver is configured

If the network driver is relying in the net core to do stats allocation,
then we want to dev_get_tstats64() instead of netdev_stats_to_stats64(),
since there are per-cpu stats that needs to be taken in consideration.

This will also simplify the drivers in regard to statistics. Once the
driver sets NETDEV_PCPU_STAT_TSTATS, it doesn't not need to allocate the
stacks, neither it needs to set `.ndo_get_stats64 = dev_get_tstats64`
for the generic stats collection function anymore.
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/core/dev.c

@@ -10702,6 +10702,8 @@ struct rtnl_link_stats64 *dev_get_stats(struct net_device *dev,
 		ops->ndo_get_stats64(dev, storage);
 	} else if (ops->ndo_get_stats) {
 		netdev_stats_to_stats64(storage, ops->ndo_get_stats(dev));
+	} else if (dev->pcpu_stat_type == NETDEV_PCPU_STAT_TSTATS) {
+		dev_get_tstats64(dev, storage);
 	} else {
 		netdev_stats_to_stats64(storage, &dev->stats);
 	}