ipv6: suppress sparse warnings in IP6_ECN_set_ce()

Pass the correct type __wsum to csum_sub() and csum_add(). This doesn't
really change anything since __wsum really *is* __be32, but removes the
address space warnings from sparse.

Cc: Eric Dumazet <edumazet@google.com>
Fixes: 34ae6a1aa054 ("ipv6: update skb->csum when CE mark is propagated")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_ecn.h

@@ -128,7 +128,8 @@ static inline int IP6_ECN_set_ce(struct sk_buff *skb, struct ipv6hdr *iph)
 	to = from | htonl(INET_ECN_CE << 20);
 	*(__be32 *)iph = to;
 	if (skb->ip_summed == CHECKSUM_COMPLETE)
-		skb->csum = csum_add(csum_sub(skb->csum, from), to);
+		skb->csum = csum_add(csum_sub(skb->csum, (__force __wsum)from),
+				     (__force __wsum)to);
 	return 1;
 }