+ * Updating builtin, hook and h is very tricky.
+ * The rules are:
+ * - builtin is only set to the current hook number
+ * if the current entry is the hook entry (aka chain
+ * head). And only for builtin chains, never for
+ * the user chains.
+ * - hook is the current hook number. If we
+ * look at user chains it needs to be NF_INET_NETNUMHOOKS.
+ * - h is the next hook entry. Thous we need to be carefully
+ * not to access the table when h is NF_INET_NETNUMHOOKS.