nixos/networkd: rename GatewayOnlink to GatewayOnLink

This follows upstreams renaming of the option [1].

[1] 9cb8c55934

nixos/doc/manual/release-notes/rl-1909.xml

@@ -104,6 +104,16 @@
       </link>
     </para>
    </listitem>
+   <listitem>
+    <para>
+      The option <option>systemd.network.networks.&lt;name&gt;.routes.*.routeConfig.GatewayOnlink</option>
+      was renamed to <option>systemd.network.networks.&lt;name&gt;.routes.*.routeConfig.GatewayOnLink</option>
+      (capital <literal>L</literal>). This follows
+      <link xlink:href="https://github.com/systemd/systemd/commit/9cb8c5593443d24c19e40bfd4fc06d672f8c554c">
+        upstreams renaming
+      </link> of the setting.
+     </para>
+   </listitem>
   </itemizedlist>
  </section>
 

nixos/modules/system/boot/networkd.nix

@@ -203,7 +203,7 @@ let
 
   checkRoute = checkUnitConfig "Route" [
     (assertOnlyFields [
-      "Gateway" "GatewayOnlink" "Destination" "Source" "Metric"
+      "Gateway" "GatewayOnLink" "Destination" "Source" "Metric"
       "IPv6Preference" "Scope" "PreferredSource" "Table" "Protocol" "Type"
       "InitialCongestionWindow" "InitialAdvertisedReceiveWindow" "QuickAck"
       "MTUBytes"

nixos/modules/tasks/network-interfaces-systemd.nix

@@ -63,7 +63,7 @@ in
               {
                 routeConfig = {
                   Gateway = gateway;
-                  GatewayOnlink = false;
+                  GatewayOnLink = false;
                 };
               }
             ];