Remove the reference to 3G icon, not sure it will fix the bug.

debian/changelog

@@ -3,7 +3,7 @@ lubuntu-artwork (0.28) UNRELEASED; urgency=low
   * usr/share/icons/lubuntu:
    - Add panel/22/nm-device-wired.svg to fix the status icon of nm-applet
      on wired and connected (LP: #976805)
-   - Possible fix for empty icon for 3G (LP: #936421)
+   - Possible fix for empty icon for 3G.
    - Add a dark icon for screenlets tray icon, from upstream.
   * usr/share/themes/Lubuntu-default:
    - Add a specific gtk theme for chromium.