By Elvira Pollina MILAN (Reuters) -Italian broadcaster MediaForEurope has joined forces with French billionaire Xavier Niel to submit a non-binding offer for a controlling stake in French TV company M6, two sources familiar with the matter said on Friday. Milan-listed MFE, previously known as Mediaset, is owned by the family of former Italian prime minister Silvio Berlusconi. Niel is the founder of French telecoms company Iliad, which also has operations in Italy. This week he announced having bought a 2.5% stake in Vodafone. One of the sources said Niel still had to decide whether to take par…