(Reuters) - Britvic Plc posted a 21.7% fall in annual operating earnings, as the British soft drink company grappled with a new law in France and wrote down the value of some assets in the country.The company, whose brands include Tango, J2O, Fruit Shoot and Teisseire, said earnings before interest and taxes (EBIT) fell to 130 million pounds ($166.79 million) for the year ended Sept. 30 from 166.1 million pounds a year earlier.Adjusted operating earnings rose 4.4% to 214.1 million pounds,..