r8152: Fix broken RX checksums.

The r8152 driver has been broken since (approx) 3.16.xx
when support was added for hardware RX checksums
on newer chip versions.  Symptoms include random
segfaults and silent data corruption over NFS.

The hardware checksum logig does not work on the VER_02
dongles I have here when used with a slow embedded system CPU.
Google reveals others reporting similar issues on Raspberry Pi.

So, disable hardware RX checksum support for VER_02, and fix
an obvious coding error for IPV6 checksums in the same function.

Because this bug results in silent data corruption,
it is a good candidate for back-porting to -stable >= 3.16.xx.
Signed-off-by: NMark Lord <mlord@pobox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/usb/r8152.c

@@ -1730,7 +1730,7 @@ static u8 r8152_rx_csum(struct r8152 *tp, struct rx_desc *rx_desc)
 	u8 checksum = CHECKSUM_NONE;
 	u32 opts2, opts3;
 
-	if (tp->version == RTL_VER_01)
+	if (tp->version == RTL_VER_01 || tp->version == RTL_VER_02)
 		goto return_result;
 
 	opts2 = le32_to_cpu(rx_desc->opts2);
@@ -1745,7 +1745,7 @@ static u8 r8152_rx_csum(struct r8152 *tp, struct rx_desc *rx_desc)
 			checksum = CHECKSUM_NONE;
 		else
 			checksum = CHECKSUM_UNNECESSARY;
-	} else if (RD_IPV6_CS) {
+	} else if (opts2 & RD_IPV6_CS) {
 		if ((opts2 & RD_UDP_CS) && !(opts3 & UDPF))
 			checksum = CHECKSUM_UNNECESSARY;
 		else if ((opts2 & RD_TCP_CS) && !(opts3 & TCPF))