match_link_modify
add_modification_hook(link_id, &match_link_modify);
add_modification_hook(link_id, &match_link_modify);
match_link_modify(sm, NULL);
static void match_link_modify(struct sm_state *sm, struct expression *mod_expr);
add_modification_hook(link_id, &match_link_modify);
add_modification_hook(link_id, &match_link_modify);