net/mlx4_en: update moderation when config reset

This patch fixes a bug that the moderation config will not be
applied when calling mlx4_en_reset_config. For example, when
turning on rx timestamping, mlx4_en_reset_config() will be called,
causing the NIC to forget previous moderation config.

This fix is in phase with a previous fix:
commit 79c54b6b ("net/mlx4_en: Fix TX moderation info loss
after set_ringparam is called")

Tested: Before this patch, on a host with NIC using mlx4, run
netserver and stream TCP to the host at full utilization.
$ sar -I SUM 1
                 INTR    intr/s
14:03:56          sum  48758.00

After rx hwtstamp is enabled:
$ sar -I SUM 1
14:10:38          sum 317771.00
We see the moderation is not working properly and issued 7x more
interrupts.

After the patch, and turned on rx hwtstamp, the rate of interrupts
is as expected:
$ sar -I SUM 1
14:52:11          sum  49332.00

Fixes: 79c54b6b ("net/mlx4_en: Fix TX moderation info loss after set_ringparam is called")
Signed-off-by: Kevin(Yudong) Yang <yyd@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
CC: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/en_ethtool.c

@@ -47,7 +47,7 @@
 #define EN_ETHTOOL_SHORT_MASK cpu_to_be16(0xffff)
 #define EN_ETHTOOL_WORD_MASK  cpu_to_be32(0xffffffff)
 
-static int mlx4_en_moderation_update(struct mlx4_en_priv *priv)
+int mlx4_en_moderation_update(struct mlx4_en_priv *priv)
 {
 	int i, t;
 	int err = 0;

drivers/net/ethernet/mellanox/mlx4/en_netdev.c

@@ -3554,6 +3554,8 @@ int mlx4_en_reset_config(struct net_device *dev,
 			en_err(priv, "Failed starting port\n");
 	}
 
+	if (!err)
+		err = mlx4_en_moderation_update(priv);
 out:
 	mutex_unlock(&mdev->state_lock);
 	kfree(tmp);

drivers/net/ethernet/mellanox/mlx4/mlx4_en.h

@@ -775,6 +775,7 @@ void mlx4_en_ptp_overflow_check(struct mlx4_en_dev *mdev);
 #define DEV_FEATURE_CHANGED(dev, new_features, feature) \
 	((dev->features & feature) ^ (new_features & feature))
 
+int mlx4_en_moderation_update(struct mlx4_en_priv *priv);
 int mlx4_en_reset_config(struct net_device *dev,
 			 struct hwtstamp_config ts_config,
 			 netdev_features_t new_features);