nfp: flower: fix used time of merge flow statistics

Prior to this change the correct value for the used counter is calculated
but not stored nor, therefore, propagated to user-space. In use-cases such
as OVS use-case at least this results in active flows being removed from
the hardware datapath. Which results in both unnecessary flow tear-down
and setup, and packet processing on the host.

This patch addresses the problem by saving the calculated used value
which allows the value to propagate to user-space.

Found by inspection.

Fixes: aa6ce2ea0c ("nfp: flower: support stats update for merge flows")
Signed-off-by: Heinrich Kuhn <heinrich.kuhn@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/flower/offload.c

@@ -1440,7 +1440,8 @@ __nfp_flower_update_merge_stats(struct nfp_app *app,
 		ctx_id = be32_to_cpu(sub_flow->meta.host_ctx_id);
 		priv->stats[ctx_id].pkts += pkts;
 		priv->stats[ctx_id].bytes += bytes;
-		max_t(u64, priv->stats[ctx_id].used, used);
+		priv->stats[ctx_id].used = max_t(u64, used,
+						 priv->stats[ctx_id].used);
 	}
 }