make BGP dummy interface addresses configurable

modules/network.nix

@@ -79,6 +79,13 @@ in {
         description = "List of IPv6 subnets to advertise via BGP";
       };
 
+      extraAddresses = mkOption {
+        type = types.listOf types.str;
+        default = [];
+        example = [ "2001:db8:0:ff::1/128" ];
+        description = "List of IP addresses to bind to the dummy interface for shared WireGuard endpoint or other HA services";
+      };
+
       routeMap = mkOption {
         type = types.enum [ "primary" "secondary" ];
         description = "BGP route map type (primary/secondary for HA)";
@@ -140,7 +147,7 @@ in {
 
     systemd.network.networks."20-shared-dummy" = mkIf cfg.bgp.enable {
       matchConfig.Name = "shared0";
-      address = [ "2600:3c08:e002:6cff::1/128" ];
+      address = cfg.bgp.extraAddresses;
     };
 
     boot.kernel.sysctl = {