gupnp_1_6: Unbreak on Darwin

All the tests except `context-filter` are broken:

    ERROR:../tests/test-context.c:265:test_gupnp_context_error_when_bound: assertion failed (error == NULL): Error binding to address 127.0.0.1:0: Operation not permitted (g-io-error-quark, 14)

    ERROR:../tests/test-context-manager.c:42:test_context_manager_manage: assertion failed (error == NULL): Failed to find IP of interface lo (gssdp-error, 0)

But we already disable them on the old `gupnp`.

pkgs/development/libraries/gupnp/1.6.nix

@@ -54,7 +54,8 @@ stdenv.mkDerivation rec {
     "-Dgtk_doc=true"
   ];
 
-  doCheck = true;
+  # On Darwin: Failed to bind socket, Operation not permitted
+  doCheck = !stdenv.hostPlatform.isDarwin;
 
   postFixup = ''
     # Cannot be in postInstall, otherwise _multioutDocs hook in preFixup will move right back.
@@ -73,6 +74,6 @@ stdenv.mkDerivation rec {
     description = "Implementation of the UPnP specification";
     mainProgram = "gupnp-binding-tool-1.6";
     license = licenses.lgpl2Plus;
-    platforms = platforms.linux;
+    platforms = platforms.unix;
   };
 }