net: core: add function for incremental IPv6 pseudo header checksum updates

Add inet_proto_csum_replace16 for incrementally updating IPv6 pseudo header
checksums for IPv6 NAT.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Acked-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/checksum.h b/include/net/checksum.h
index ba55d8b..600d1d7 100644
--- a/include/net/checksum.h
+++ b/include/net/checksum.h
@@ -109,6 +109,9 @@
 struct sk_buff;
 extern void inet_proto_csum_replace4(__sum16 *sum, struct sk_buff *skb,
 				     __be32 from, __be32 to, int pseudohdr);
+extern void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb,
+				      const __be32 *from, const __be32 *to,
+				      int pseudohdr);
 
 static inline void inet_proto_csum_replace2(__sum16 *sum, struct sk_buff *skb,
 					    __be16 from, __be16 to,