[NET]: Annotate skb_checksum() and callers.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 6e8c15b..be9b541 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1240,8 +1240,8 @@
 
 /* Checksum skb data. */
 
-unsigned int skb_checksum(const struct sk_buff *skb, int offset,
-			  int len, unsigned int csum)
+__wsum skb_checksum(const struct sk_buff *skb, int offset,
+			  int len, __wsum csum)
 {
 	int start = skb_headlen(skb);
 	int i, copy = start - offset;