tb_switch_find_by_link_depth
sw = tb_switch_find_by_link_depth(tb, link, depth);
sw = tb_switch_find_by_link_depth(tb, link, depth);
sw = tb_switch_find_by_link_depth(tb, dual_link, depth);
parent_sw = tb_switch_find_by_link_depth(tb, link, depth - 1);
sw = tb_switch_find_by_link_depth(tb, link, depth);
struct tb_switch *tb_switch_find_by_link_depth(struct tb *tb, u8 link,