igb: count Rx FIFO errors correctly

Don't aggregate rx_no_buffer_count into rx_fifo_errors. RNBC counts
packets that get queued temporarily in the adapter's FIFO. These
packets are not dropped and are not errors. The correct counter
is rx_missed_errors (MPC).
Signed-off-by: NMitch Williams <mitch.a.williams@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/igb/igb_main.c

@@ -3963,7 +3963,7 @@ void igb_update_stats(struct igb_adapter *adapter)
 	struct net_device_stats *net_stats = igb_get_stats(adapter->netdev);
 	struct e1000_hw *hw = &adapter->hw;
 	struct pci_dev *pdev = adapter->pdev;
-	u32 rnbc, reg;
+	u32 reg, mpc;
 	u16 phy_tmp;
 	int i;
 	u64 bytes, packets;
@@ -4021,7 +4021,9 @@ void igb_update_stats(struct igb_adapter *adapter)
 	adapter->stats.symerrs += rd32(E1000_SYMERRS);
 	adapter->stats.sec += rd32(E1000_SEC);
 
-	adapter->stats.mpc += rd32(E1000_MPC);
+	mpc = rd32(E1000_MPC);
+	adapter->stats.mpc += mpc;
+	net_stats->rx_fifo_errors += mpc;
 	adapter->stats.scc += rd32(E1000_SCC);
 	adapter->stats.ecol += rd32(E1000_ECOL);
 	adapter->stats.mcc += rd32(E1000_MCC);
@@ -4036,9 +4038,7 @@ void igb_update_stats(struct igb_adapter *adapter)
 	adapter->stats.gptc += rd32(E1000_GPTC);
 	adapter->stats.gotc += rd32(E1000_GOTCL);
 	rd32(E1000_GOTCH); /* clear GOTCL */
-	rnbc = rd32(E1000_RNBC);
-	adapter->stats.rnbc += rnbc;
-	net_stats->rx_fifo_errors += rnbc;
+	adapter->stats.rnbc += rd32(E1000_RNBC);
 	adapter->stats.ruc += rd32(E1000_RUC);
 	adapter->stats.rfc += rd32(E1000_RFC);
 	adapter->stats.rjc += rd32(E1000_RJC);