+ * SIOCSETROUTERMODE_IN6
+ * Set the IPv6 router mode on an interface.
+ *
+ * IPV6_ROUTER_MODE_DISABLED
+ * - disable IPv6 router mode if it is enabled
+ * - if the previous mode was IPV6_ROUTER_MODE_EXCUSIVE,
+ * scrubs all IPv6 auto-configured addresses
+ *
+ * IPV6_ROUTER_MODE_EXCLUSIVE
+ * - act exclusively as an IPv6 router on the interface
+ * - disables accepting external Router Advertisements
+ * - scrubs all IPv6 auto-configured addresses
+ * - disables optimistic dad
+ * - disables ND6 prefix proxy, if enabled
+ * - used by the internet sharing/personal hotspot feature
+ *
+ * IPV6_ROUTER_MODE_HYBRID
+ * - act as both an IPv6 router and IPv6 client on the interface
+ * - does not modify whether to accept Router Advertisements
+ * - does not scrub any addresses
+ * - used when acting as the gateway/router for an otherwise isolated
+ * network whose existence is likely advertised via a
+ * a Route Information Option in a Router Advertisement