Specifies how the wan gets its IPV6 address.
auto-configuration - auto get ipv6 address by RFC about IPV6
static - Statically assigned IPV6 address
when ipv6addr mode from auto-configuration to static,the relative nodes should be set together ,
including:ruckusDeviceWanIPV6Addr,ruckusDeviceWanIPV6PrefixLen,ruckusDeviceWanIPV6Gateway