nf_checksum
__sum16 nf_checksum(struct sk_buff *skb, unsigned int hook,
nf_checksum(skb, state->hook, dataoff, IPPROTO_TCP, state->pf)) {
nf_checksum(skb, state->hook, dataoff, IPPROTO_UDP, state->pf)) {
EXPORT_SYMBOL_GPL(nf_checksum);