tcp: Call gso_make_checksum

Call common gso_make_checksum when calculating checksum for a
TCP GSO segment.
Signed-off-by: NTom Herbert <therbert@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_offload.c

@@ -97,9 +97,7 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
 		th->check = newcheck;
 
 		if (skb->ip_summed != CHECKSUM_PARTIAL)
-			th->check =
-			     csum_fold(csum_partial(skb_transport_header(skb),
-						    thlen, skb->csum));
+			th->check = gso_make_checksum(skb, ~th->check);
 
 		seq += mss;
 		if (copy_destructor) {
@@ -133,8 +131,7 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
 	th->check = ~csum_fold((__force __wsum)((__force u32)th->check +
 				(__force u32)delta));
 	if (skb->ip_summed != CHECKSUM_PARTIAL)
-		th->check = csum_fold(csum_partial(skb_transport_header(skb),
-						   thlen, skb->csum));
+		th->check = gso_make_checksum(skb, ~th->check);
 out:
 	return segs;
 }