By Elvira Pollina MILAN (Reuters) -Telecom Italia (TIM) is considering selling its stake in mobile tower group INWIT to French investment fund Ardian as part of its efforts to shore up its finances, a source close to the matter said on Wednesday. Under such a potential deal, first reported by Italian daily La Repubblica, debt-laden TIM could raise 1.3 billion euros ($1.5 billion) from the sale of its 15.4% indirect stake in Milan-listed INWIT, based on current market value. Telecom Italia and Ardian, which already owns a 15% indirect holding in INWIT, declined to comment. The potential INWIT s…