machines/styx: hand gg23 routing over to acheron
styx keeps hass/snapserver/mycelium as a plain LAN client on et0 with a
static lease (10.42.0.3) from acheron; 10.42.0.1 now means the router.
Repoint snapclient, mycelium peers, zigbee2mqtt broker, ignavia's tinc
Address and the gg23 extraHosts accordingly.