hsr_get_max_mtu
if (new_mtu > hsr_get_max_mtu(hsr)) {
int hsr_get_max_mtu(struct hsr_priv *hsr);
mtu_max = hsr_get_max_mtu(port->hsr);
dev_set_mtu(master->dev, hsr_get_max_mtu(hsr));
dev_set_mtu(master->dev, hsr_get_max_mtu(hsr));