Fixed downlink processing of spgw.p4

Change-Id: I37f2361bcdd6539a38b294b7da10989a851cf2ec
diff --git a/pipelines/fabric/src/main/resources/include/checksum.p4 b/pipelines/fabric/src/main/resources/include/checksum.p4
index 4d1782d..d920235 100644
--- a/pipelines/fabric/src/main/resources/include/checksum.p4
+++ b/pipelines/fabric/src/main/resources/include/checksum.p4
@@ -43,7 +43,8 @@
             HashAlgorithm.csum16
         );
 #ifdef WITH_SPGW
-        update_gtpu_checksum.apply(hdr.gtpu_ipv4);
+        update_gtpu_checksum.apply(hdr.gtpu_ipv4, hdr.gtpu_udp, hdr.gtpu,
+                                   hdr.ipv4, hdr.udp);
 #endif // WITH_SPGW
     }
 }