BRUSSELS — The European Union wants to stop Russian gas tankers from using a Belgian port to transport shipments of non-Russian gas around the world, in an effort to finally sever ties with the country's energy shipping fleet. As the EU has progressively ratcheted up sanctions on Russian gas entering Europe in an effort to shrink the Kremlin's war chest, one part of the Russian shipping sector has fallen through the cracks. So-called transshipment services — whereby ports offer long-term "slots"