i40e: remove hardcode of stats struct size in ethtool

Base the queue stats length on the queue stats struct rather than
assuming it is 2 fields.  This is in prep for adding data fields
which are configuration dependent.

Change-ID: I937f471f389d2e0f8cec733960c5d9a06b14f3ec
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_ethtool.c

@@ -122,8 +122,9 @@ static struct i40e_stats i40e_gstrings_stats[] = {
 };
 
 #define I40E_QUEUE_STATS_LEN(n) \
-  ((((struct i40e_netdev_priv *)netdev_priv((n)))->vsi->num_queue_pairs + \
-    ((struct i40e_netdev_priv *)netdev_priv((n)))->vsi->num_queue_pairs) * 2)
+	(((struct i40e_netdev_priv *)netdev_priv((n)))->vsi->num_queue_pairs \
+	    * 2 /* Tx and Rx together */                                     \
+	    * (sizeof(struct i40e_queue_stats) / sizeof(u64)))
 #define I40E_GLOBAL_STATS_LEN	ARRAY_SIZE(i40e_gstrings_stats)
 #define I40E_NETDEV_STATS_LEN   ARRAY_SIZE(i40e_gstrings_net_stats)
 #define I40E_VSI_STATS_LEN(n)   (I40E_NETDEV_STATS_LEN + \