Driver drop incoming packets >= 1515(1) if MTU is set between 1515(1) and 1536.

1) exact number depends on some factors:
- VLAN tagged or not
- patch "r8169: Fix card drop incoming VLAN tagged MTU byte large jumbo frames"
  applied or not

Bonus: got rid of magic number 8

Signed-off-by: Raimonds Cicans <ray@apollo.lv>

---

--- linux-2.6.31/drivers/net/r8169.c.orig	2009-11-06 21:52:12.722326601 +0200
+++ linux-2.6.31/drivers/net/r8169.c	2009-11-06 22:09:17.242224014 +0200
@@ -2229,9 +2229,9 @@ static void __devexit rtl8169_remove_one
 static void rtl8169_set_rxbufsize(struct rtl8169_private *tp,
 				  struct net_device *dev)
 {
-	unsigned int mtu = dev->mtu;
+	unsigned int max_frame = dev->mtu + VLAN_ETH_HLEN + ETH_FCS_LEN;
 
-	tp->rx_buf_sz = (mtu > RX_BUF_SIZE) ? mtu + ETH_HLEN + 8 : RX_BUF_SIZE;
+	tp->rx_buf_sz = (max_frame > RX_BUF_SIZE) ? max_frame : RX_BUF_SIZE;
 }
 
 static int rtl8169_open(struct net_device *dev)