Chinese e-commerce giant Alibaba is seeking to sell its entire stake in Mango Excellent Media, less than a year after buying stock shares from the company. The move comes as Beijing has tightened its grip over various industries, including e-commerce. Television-based service provider Mango Excellent Media, headquartered in Hunan Province, announced on Sept. 24 that an investment arm of Alibaba Group Holding Ltd. proposed to sell the entire 5.01 percent shares of the broadcaster, according to the company’s filing to Shenzhen Stock Exchange. The shares were valued at about $600 million based on Thursday’s closing price. However, the tech giant paid $960 million when it bought the shares nine months ago. Alibaba is seeking a waiver from a one-year lockup agreement, the filing showed. The agreed period ends on Dec. 26, 2021. The document didn’t reveal the proposed selling price, yet shares of the media company have fallen roughly 40 percent since Alibaba’s investment …