ixgbe: fix issues setting rx-usecs with legacy interrupts

Currently setting rx-usecs when the interface is in legacy interrupt
mode it is not immediate.  We were only setting EITR for each MSIx
vector and since this count would be zero for legacy mode it wasn't
set until after a reset.  This patch corrects that by checking what
mode we are in and then setting EITR accordingly.
Signed-off-by: Don Skidmore <donald.skidmore@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ixgbe/ixgbe_ethtool.c

@@ -1948,6 +1948,7 @@ static int ixgbe_set_coalesce(struct net_device *netdev,
                               struct ethtool_coalesce *ec)
 {
 	struct ixgbe_adapter *adapter = netdev_priv(netdev);
+	struct ixgbe_q_vector *q_vector;
 	int i;
 
 	if (ec->tx_max_coalesced_frames_irq)
@@ -1982,8 +1983,12 @@ static int ixgbe_set_coalesce(struct net_device *netdev,
 		adapter->itr_setting = 0;
 	}
 
-	for (i = 0; i < adapter->num_msix_vectors - NON_Q_VECTORS; i++) {
-		struct ixgbe_q_vector *q_vector = adapter->q_vector[i];
+	/* MSI/MSIx Interrupt Mode */
+	if (adapter->flags &
+	    (IXGBE_FLAG_MSIX_ENABLED | IXGBE_FLAG_MSI_ENABLED)) {
+		int num_vectors = adapter->num_msix_vectors - NON_Q_VECTORS;
+		for (i = 0; i < num_vectors; i++) {
+			q_vector = adapter->q_vector[i];
 			if (q_vector->txr_count && !q_vector->rxr_count)
 				/* tx vector gets half the rate */
 				q_vector->eitr = (adapter->eitr_param >> 1);
@@ -1992,6 +1997,12 @@ static int ixgbe_set_coalesce(struct net_device *netdev,
 				q_vector->eitr = adapter->eitr_param;
 			ixgbe_write_eitr(q_vector);
 		}
+	/* Legacy Interrupt Mode */
+	} else {
+		q_vector = adapter->q_vector[0];
+		q_vector->eitr = adapter->eitr_param;
+		ixgbe_write_eitr(q_vector);
+	}
 
 	return 0;
 }