8139cp: fix checksum broken

I am not family with RealTek RTL-8139C+ series 10/100 PCI Ethernet driver.
I try to guess the meaning of RxProtoIP and IPFail.
RxProtoIP stands for received IPv4 packet that upper protocol is not tcp and udp.
!(status & IPFail) is true means that driver correctly to check checksum in IPv4 header.

If these are right, driver will set ip_summed with CHECKSUM_UNNECESSARY for other
upper protocol, e.g. sctp, igmp protocol. This will cause protocol stack ignores
checksum check for packets with invalid checksum.

This patch is only compile-test.
Signed-off-by: NShan Wei <shanwei@cn.fujitsu.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/8139cp.c

@@ -490,13 +490,11 @@ static inline unsigned int cp_rx_csum_ok (u32 status)
 {
 	unsigned int protocol = (status >> 16) & 0x3;
 
-	if (likely((protocol == RxProtoTCP) && (!(status & TCPFail))))
+	if (((protocol == RxProtoTCP) && !(status & TCPFail)) ||
+	    ((protocol == RxProtoUDP) && !(status & UDPFail)))
 		return 1;
-	else if ((protocol == RxProtoUDP) && (!(status & UDPFail)))
-		return 1;
-	else if ((protocol == RxProtoIP) && (!(status & IPFail)))
-		return 1;
-	return 0;
+	else
+		return 0;
 }
 
 static int cp_rx_poll(struct napi_struct *napi, int budget)