nixos/dhcpcd: add IPv6rs option

nixos/doc/manual/release-notes/rl-2305.section.md

@@ -284,6 +284,7 @@ In addition to numerous new and upgraded packages, this release has the followin
   ```
 
 - `services.dhcpcd` service now don't solicit or accept IPv6 Router Advertisements on interfaces that use static IPv6 addresses.
+  If network uses both IPv6 Unique local addresses (ULA) and global IPv6 address auto-configuration with SLAAC, must add the parameter `networking.dhcpcd.IPv6rs = true;`.
 
 - The module `services.headscale` was refactored to be compliant with [RFC 0042](https://github.com/NixOS/rfcs/blob/master/rfcs/0042-config-option.md). To be precise, this means that the following things have changed:
 

nixos/modules/services/networking/dhcpcd.nix

@@ -81,9 +81,12 @@ let
         noipv6
       ''}
 
-      ${cfg.extraConfig}
+      ${optionalString (config.networking.enableIPv6 && cfg.IPv6rs == null && staticIPv6Addresses != [ ]) noIPv6rs}
+      ${optionalString (config.networking.enableIPv6 && cfg.IPv6rs == false) ''
+        noipv6rs
+      ''}
 
-      ${optionalString config.networking.enableIPv6 noIPv6rs}
+      ${cfg.extraConfig}
     '';
 
   exitHook = pkgs.writeText "dhcpcd.exit-hook"
@@ -160,6 +163,16 @@ in
       '';
     };
 
+    networking.dhcpcd.IPv6rs = mkOption {
+      type = types.nullOr types.bool;
+      default = null;
+      description = lib.mdDoc ''
+        Force enable or disable solicitation and receipt of IPv6 Router Advertisements.
+        This is required, for example, when using a static unique local IPv6 address (ULA)
+        and global IPv6 address auto-configuration with SLAAC.
+      '';
+    };
+
     networking.dhcpcd.runHook = mkOption {
       type = types.lines;
       default = "";