r8169: use PCI define for Max_Read_Request_Size

Replace a magic number with a PCI #define symbol.
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/r8169.c

@@ -4915,7 +4915,7 @@ static void r8168c_hw_jumbo_enable(struct rtl8169_private *tp)
 
 	RTL_W8(Config3, RTL_R8(Config3) | Jumbo_En0);
 	RTL_W8(Config4, RTL_R8(Config4) | Jumbo_En1);
-	rtl_tx_performance_tweak(tp->pci_dev, 0x2 << MAX_READ_REQUEST_SHIFT);
+	rtl_tx_performance_tweak(tp->pci_dev, PCI_EXP_DEVCTL_READRQ_512B);
 }
 
 static void r8168c_hw_jumbo_disable(struct rtl8169_private *tp)
@@ -4948,7 +4948,7 @@ static void r8168e_hw_jumbo_enable(struct rtl8169_private *tp)
 	RTL_W8(MaxTxPacketSize, 0x3f);
 	RTL_W8(Config3, RTL_R8(Config3) | Jumbo_En0);
 	RTL_W8(Config4, RTL_R8(Config4) | 0x01);
-	rtl_tx_performance_tweak(tp->pci_dev, 0x2 << MAX_READ_REQUEST_SHIFT);
+	rtl_tx_performance_tweak(tp->pci_dev, PCI_EXP_DEVCTL_READRQ_512B);
 }
 
 static void r8168e_hw_jumbo_disable(struct rtl8169_private *tp)
@@ -4964,7 +4964,7 @@ static void r8168e_hw_jumbo_disable(struct rtl8169_private *tp)
 static void r8168b_0_hw_jumbo_enable(struct rtl8169_private *tp)
 {
 	rtl_tx_performance_tweak(tp->pci_dev,
-		(0x2 << MAX_READ_REQUEST_SHIFT) | PCI_EXP_DEVCTL_NOSNOOP_EN);
+		PCI_EXP_DEVCTL_READRQ_512B | PCI_EXP_DEVCTL_NOSNOOP_EN);
 }
 
 static void r8168b_0_hw_jumbo_disable(struct rtl8169_private *tp)