nixos/unifi: Explain and simplify the bind mount configuration

nixos/modules/services/networking/unifi.nix

@@ -27,30 +27,28 @@ in
       home = "${stateDir}";
     };
 
-    systemd.mounts = [
+    # We must create the binary directories as bind mounts instead of symlinks
-      {
+    # This is because the controller resolves all symlinks to absolute paths
+    # to be used as the working directory.
+    systemd.mounts = map ({ what, where }: {
         bindsTo = [ "unifi.service" ];
         requiredBy = [ "unifi.service" ];
         before = [ "unifi.service" ];
+        options = "bind";
+        what = what;
+        where = where;
+      }) [
+        {
           what = "${pkgs.unifi}/dl";
           where = "${stateDir}/dl";
-        options = "bind";
         }
         {
-        bindsTo = [ "unifi.service" ];
-        requiredBy = [ "unifi.service" ];
-        before = [ "unifi.service" ];
           what = "${pkgs.unifi}/lib";
           where = "${stateDir}/lib";
-        options = "bind";
         }
         {
-        bindsTo = [ "unifi.service" ];
-        requiredBy = [ "unifi.service" ];
-        before = [ "unifi.service" ];
           what = "${pkgs.mongodb}/bin";
           where = "${stateDir}/bin";
-        options = "bind";
         }
       ];