igb: Use a 32-bit mask when calculating the flow control watermarks

For some devices, the result of the flow control high watermark gets
truncated when programming it into the registers because of the mask used.
Switch the mask to 32-bit to prevent this from happening.
Signed-off-by: Matthew Vick <matthew.vick@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -1589,8 +1589,7 @@ void igb_reset(struct igb_adapter *adapter)
 	struct e1000_hw *hw = &adapter->hw;
 	struct e1000_mac_info *mac = &hw->mac;
 	struct e1000_fc_info *fc = &hw->fc;
-	u32 pba = 0, tx_space, min_tx_space, min_rx_space;
-	u16 hwm;
+	u32 pba = 0, tx_space, min_tx_space, min_rx_space, hwm;
 
 	/* Repartition Pba for greater than 9k mtu
 	 * To take effect CTRL.RST is required.
@@ -1665,7 +1664,7 @@ void igb_reset(struct igb_adapter *adapter)
 	hwm = min(((pba << 10) * 9 / 10),
 			((pba << 10) - 2 * adapter->max_frame_size));
 
-	fc->high_water = hwm & 0xFFF0;	/* 16-byte granularity */
+	fc->high_water = hwm & 0xFFFFFFF0;	/* 16-byte granularity */
 	fc->low_water = fc->high_water - 16;
 	fc->pause_time = 0xFFFF;
 	fc->send_xon = 1;