datapath-windows:Correct checksum for DNAT action

While testing OVS-windows flows for the DNAT action, the checksum
In TCP header is set incorrectly when TCP offload is enabled by
Default. As a result, the packet will be dropped on receiver linuxVM.

>>>sample flow default configuration on both Windows VM and Linux VM
(src=40.0.1.2,dst=10.150.0.1) --dnat--> (src=40.0.1.2,dst==30.1.0.2)
Without the fix for some TCP packet(40.0.1.2->30.1.0.2 with payload
len 207) the TCP checksum will be pseduo header checksum and the value
is 0x01d6. With the fix the checksum will be 0x47ee, it could be got
the correct TCP checksum on the receiver Linux VM.

Signed-off-by: Wilson Peng<pweisong@vmware.com>
Signed-off-by: Anand Kumar<kumaranand@vmware.com>
Acked-by: Alin-Gabriel Serdean <aserdean@ovn.org>
Signed-off-by: Alin-Gabriel Serdean <aserdean@ovn.org>

datapath-windows/ovsext/Actions.c

@@ -1550,9 +1550,21 @@ OvsUpdateAddressAndPort(OvsForwardingContext *ovsFwdCtx,
         if (tcpHdr) {
             portField = &tcpHdr->dest;
             checkField = &tcpHdr->check;
+            l4Offload = isTx ? (BOOLEAN)csumInfo.Transmit.TcpChecksum :
+                        ((BOOLEAN)csumInfo.Receive.TcpChecksumSucceeded ||
+                         (BOOLEAN)csumInfo.Receive.TcpChecksumFailed);
         } else if (udpHdr) {
             portField = &udpHdr->dest;
             checkField = &udpHdr->check;
+            l4Offload = isTx ? (BOOLEAN)csumInfo.Transmit.UdpChecksum :
+                        ((BOOLEAN)csumInfo.Receive.UdpChecksumSucceeded ||
+                         (BOOLEAN)csumInfo.Receive.UdpChecksumFailed);
+        }
+
+       if (l4Offload) {
+            *checkField = IPPseudoChecksum(&ipHdr->saddr, &newAddr,
+                tcpHdr ? IPPROTO_TCP : IPPROTO_UDP,
+                ntohs(ipHdr->tot_len) - ipHdr->ihl * 4);
         }
     }