pfil_link_remove
static struct pfil_link *pfil_link_remove(pfil_chain_t *, pfil_hook_t );
in = pfil_link_remove(&head->head_in, hook);
out = pfil_link_remove(&head->head_out, hook);
in = pfil_link_remove(&head->head_in, hook);
out = pfil_link_remove(&head->head_out, hook);