net: checksum: fix warning in skb_checksum

This patch fixes a build warning in skb_checksum() by wrapping the
csum_partial() usage in skb_checksum(). The problem is that on a few
architectures, csum_partial is used with prefix asmlinkage whereas
on most architectures it's not. So fix this up generically as we did
with csum_block_add_ext() to match the signature. Introduced by
2817a336d4 ("net: skb_checksum: allow custom update/combine for
walking skb").

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -2003,7 +2003,7 @@ __wsum skb_checksum(const struct sk_buff *skb, int offset,
 		    int len, __wsum csum)
 {
 	const struct skb_checksum_ops ops = {
-		.update  = csum_partial,
+		.update  = csum_partial_ext,
 		.combine = csum_block_add_ext,
 	};