e1000e: Fix CRC errors with jumbo traffic

Modifying the jumbo frame workaround for 82579, i217 and i218 client parts
to increase the gap between the read and write pointers in the Tx FIFO.
Signed-off-by: Dave Ertman <david.m.ertman@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/e1000e/defines.h

@@ -342,6 +342,7 @@
 #define E1000_TIPG_IPGR2_SHIFT  20
 
 #define MAX_JUMBO_FRAME_SIZE    0x3F00
+#define E1000_TX_PTR_GAP		0x1F
 
 /* Extended Configuration Control and Size */
 #define E1000_EXTCNF_CTRL_MDIO_SW_OWNERSHIP      0x00000020

drivers/net/ethernet/intel/e1000e/ich8lan.c

@@ -2444,7 +2444,7 @@ s32 e1000_lv_jumbo_workaround_ich8lan(struct e1000_hw *hw, bool enable)
 			return ret_val;
 		e1e_rphy(hw, PHY_REG(776, 20), &data);
 		data &= ~(0x3FF << 2);
-		data |= (0x1A << 2);
+		data |= (E1000_TX_PTR_GAP << 2);
 		ret_val = e1e_wphy(hw, PHY_REG(776, 20), data);
 		if (ret_val)
 			return ret_val;