net/sctp: Refactor SCTP skb checksum computation

This patch consolidates the SCTP checksum calculation code from various
places to a single new function, sctp_compute_cksum(skb, offset).

Signed-off-by: Joe Stringer <joe@wand.net.nz>
Reviewed-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sctp/input.c b/net/sctp/input.c
index 7993495..fa91aff 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -87,15 +87,7 @@
 {
 	struct sctphdr *sh = sctp_hdr(skb);
 	__le32 cmp = sh->checksum;
-	struct sk_buff *list;
-	__le32 val;
-	__u32 tmp = sctp_start_cksum((__u8 *)sh, skb_headlen(skb));
-
-	skb_walk_frags(skb, list)
-		tmp = sctp_update_cksum((__u8 *)list->data, skb_headlen(list),
-					tmp);
-
-	val = sctp_end_cksum(tmp);
+	__le32 val = sctp_compute_cksum(skb, 0);
 
 	if (val != cmp) {
 		/* CRC failure, dump it. */