icmp_push_reply(): reorder adding the checksum up

do csum_partial_copy_nocheck() on the first fragment, then
add the rest to it.  Equivalent transformation.

That was the only caller of csum_partial_copy_nocheck() that
might pass it non-zero as the last argument.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

net/ipv4/icmp.c

@@ -376,15 +376,15 @@ static void icmp_push_reply(struct icmp_bxm *icmp_param,
 		ip_flush_pending_frames(sk);
 	} else if ((skb = skb_peek(&sk->sk_write_queue)) != NULL) {
 		struct icmphdr *icmph = icmp_hdr(skb);
-		__wsum csum = 0;
+		__wsum csum;
 		struct sk_buff *skb1;
 
+		csum = csum_partial_copy_nocheck((void *)&icmp_param->data,
+						 (char *)icmph,
+						 icmp_param->head_len, 0);
 		skb_queue_walk(&sk->sk_write_queue, skb1) {
 			csum = csum_add(csum, skb1->csum);
 		}
-		csum = csum_partial_copy_nocheck((void *)&icmp_param->data,
-						 (char *)icmph,
-						 icmp_param->head_len, csum);
 		icmph->checksum = csum_fold(csum);
 		skb->ip_summed = CHECKSUM_NONE;
 		ip_push_pending_frames(sk, fl4);