MTAG_FIREWIRE_HWADDR
mtag = m_tag_locate(m, MTAG_FIREWIRE, MTAG_FIREWIRE_HWADDR, 0);
mtag = m_tag_locate(m, MTAG_FIREWIRE, MTAG_FIREWIRE_HWADDR, NULL);
mtag = m_tag_alloc(MTAG_FIREWIRE, MTAG_FIREWIRE_HWADDR,