i40e: Fix Rx checksum error counter

The Rx port checksum error counter was incrementing incorrectly with
UDP encapsulated tunneled traffic.  This patch fixes the problem so that
the port_rx_csum counter will show accurate statistics.
Signed-off-by: Anjali Singhai <anjali.singhai@intel.com>
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -1325,9 +1325,7 @@ static inline void i40e_rx_checksum(struct i40e_vsi *vsi,
 	 * so the total length of IPv4 header is IHL*4 bytes
 	 * The UDP_0 bit *may* bet set if the *inner* header is UDP
 	 */
-	if (ipv4_tunnel &&
-	    (decoded.inner_prot != I40E_RX_PTYPE_INNER_PROT_UDP) &&
-	    !(rx_status & (1 << I40E_RX_DESC_STATUS_UDP_0_SHIFT))) {
+	if (ipv4_tunnel) {
 		skb->transport_header = skb->mac_header +
 					sizeof(struct ethhdr) +
 					(ip_hdr(skb)->ihl * 4);
@@ -1337,15 +1335,19 @@ static inline void i40e_rx_checksum(struct i40e_vsi *vsi,
 					  skb->protocol == htons(ETH_P_8021AD))
 					  ? VLAN_HLEN : 0;
 
-		rx_udp_csum = udp_csum(skb);
-		iph = ip_hdr(skb);
-		csum = csum_tcpudp_magic(
-				iph->saddr, iph->daddr,
-				(skb->len - skb_transport_offset(skb)),
-				IPPROTO_UDP, rx_udp_csum);
+		if ((ip_hdr(skb)->protocol == IPPROTO_UDP) &&
+		    (udp_hdr(skb)->check != 0)) {
+			rx_udp_csum = udp_csum(skb);
+			iph = ip_hdr(skb);
+			csum = csum_tcpudp_magic(
+					iph->saddr, iph->daddr,
+					(skb->len - skb_transport_offset(skb)),
+					IPPROTO_UDP, rx_udp_csum);
 
-		if (udp_hdr(skb)->check != csum)
-			goto checksum_fail;
+			if (udp_hdr(skb)->check != csum)
+				goto checksum_fail;
+
+		} /* else its GRE and so no outer UDP header */
 	}
 
 	skb->ip_summed = CHECKSUM_UNNECESSARY;