feat: overwrite IPv6 interface id for DynDNS for melissa

devices/melissa.nix

@@ -33,7 +33,21 @@ melissa: my desktop PC
   };
 
   eisfunke.domains = [
-    { domain = "eisfunke.com"; subs = [ "melissa" ]; type = "ipv6"; }
+    {
+      domain = "eisfunke.com";
+      subs = [ "melissa" ];
+      type = "ipv6";
+      /*
+      - melissa uses IPv6 privacy extensions on a residential internet connection
+      - so it will put that IP into DNS
+      - problem is: that IP is changing regularly, so I can't open it in the firewall
+      - the non-privacy-extension IP is still valid for incoming connection, so I can just put that
+        into DNS
+      - I do that by overwriting the interface id (i.e. the second half) in the detected public IPv6
+        with the non-privacy-extension-one derived from the MAC address
+      */
+      ipv6OverwriteInterfaceId = "b62e:99ff:fee2:0f10";
+    }
   ];
 
   networking.hostName = "melissa";