net: export a helper for adding up queue stats

[ Upstream commit 23fa6a23d97182d36ca3c71e43c804fa91e46a03 ]

Older drivers and drivers with lower queue counts often have a static
array of queues, rather than allocating structs for each queue on demand.
Add a helper for adding up qstats from a queue range. Expectation is
that driver will pass a queue range [netdev->real_num_*x_queues, MAX).
It was tempting to always use num_*x_queues as the end, but virtio
seems to clamp its queue count after allocating the netdev. And this
way we can trivaly reuse the helper for [0, real_..).

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20250507003221.823267-2-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Stable-dep-of: 001160ec8c59 ("virtio-net: fix total qstat values")
Signed-off-by: Sasha Levin <sashal@kernel.org>

include/net/netdev_queues.h

@@ -92,6 +92,12 @@ struct netdev_stat_ops {
 			       struct netdev_queue_stats_tx *tx);
 };
 
+void netdev_stat_queue_sum(struct net_device *netdev,
+			   int rx_start, int rx_end,
+			   struct netdev_queue_stats_rx *rx_sum,
+			   int tx_start, int tx_end,
+			   struct netdev_queue_stats_tx *tx_sum);
+
 /**
  * struct netdev_queue_mgmt_ops - netdev ops for queue management
  *