ixgbe: Set Drop_EN bit when multiple Rx queues are present w/o flow control

The drop enable bit can be used to improve the performance of the adapter
in the case of multiple queues being present.  This performance gain is due
to the fact that some slower CPUs can cause the FIFO to backfill preventing
faster CPUs from receiving additional work.  By setting the drop enable bit
we prevent this and instead just drop the packets that would have been
bound for the slower CPU.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe.h

@@ -652,6 +652,7 @@ extern void ixgbe_atr_compute_perfect_hash_82599(union ixgbe_atr_input *input,
 						 union ixgbe_atr_input *mask);
 extern void ixgbe_set_rx_mode(struct net_device *netdev);
 #ifdef CONFIG_IXGBE_DCB
+extern void ixgbe_set_rx_drop_en(struct ixgbe_adapter *adapter);
 extern int ixgbe_setup_tc(struct net_device *dev, u8 tc);
 #endif
 extern void ixgbe_tx_ctxtdesc(struct ixgbe_ring *, u32, u32, u32, u32);