net: socionext: use new helper tcp_v6_gso_csum_prep

Use new helper tcp_v6_gso_csum_prep in additional network drivers.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/socionext/netsec.c

@@ -1148,11 +1148,7 @@ static netdev_tx_t netsec_netdev_start_xmit(struct sk_buff *skb,
 				~tcp_v4_check(0, ip_hdr(skb)->saddr,
 					      ip_hdr(skb)->daddr, 0);
 		} else {
-			ipv6_hdr(skb)->payload_len = 0;
-			tcp_hdr(skb)->check =
-				~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
-						 &ipv6_hdr(skb)->daddr,
-						 0, IPPROTO_TCP, 0);
+			tcp_v6_gso_csum_prep(skb);
 		}
 
 		tx_ctrl.tcp_seg_offload_flag = true;