[IPV4/IPV6]: In ip_fragment(), reset ip_summed field on SKB sub-frags.

If we forward a fragmented packet, we can have ip_summed
set to CHECKSUM_HW or similar.  This is fine for local
protocol processing, but once if we are forwarding this
packet we want to reset ip_summed to CHECKSUM_NONE.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_output.c

@@ -504,6 +504,7 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff*))
 			/* Prepare header of the next frame,
 			 * before previous one went down. */
 			if (frag) {
+				frag->ip_summed = CHECKSUM_NONE;
 				frag->h.raw = frag->data;
 				frag->nh.raw = __skb_push(frag, hlen);
 				memcpy(frag->nh.raw, iph, hlen);

net/ipv6/ip6_output.c

@@ -592,6 +592,7 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 			/* Prepare header of the next frame,
 			 * before previous one went down. */
 			if (frag) {
+				frag->ip_summed = CHECKSUM_NONE;
 				frag->h.raw = frag->data;
 				fh = (struct frag_hdr*)__skb_push(frag, sizeof(struct frag_hdr));
 				frag->nh.raw = __skb_push(frag, hlen);