vec_validate_init_empty (cm->config_index_by_sw_if_index, sw_if_index, ~0);
ci = cm->config_index_by_sw_if_index[sw_if_index];
vec_validate_init_empty (cm->config_index_by_sw_if_index, sw_if_index, ~0);
ci = cm->config_index_by_sw_if_index[sw_if_index];