system-config-network-1.3.22-1 does not support configuring 6in4 (sit) IPv6 tunneling devices. Required files are ifcfg-sit*, parameters are TYPE, DEVICE, IPV6ADDR, IPV6TUNNELIPV4, IPV6INIT and ONBOOT.
https://hosted.fedoraproject.org/projects/system-config-network/ticket/39