There is something mournful in the sight of two once-mighty handset makers battling each other in the law courts, chasing licensing revenues to help compensate for the collapse of their device businesses. BlackBerry has sued Nokia in federal court in Delaware, claiming the Finnish giant is infringing on as many as 11 of its patents in its RAN equipment. Both firms have significant stockpiles of patents, and their attempts to monetize these more effectively have brought them into conflict with several former product rivals as well as other firms. BlackBerry set up a patents licensing unit in 2014 and sued Avaya and Blu Products last summer, while Nokia has embarked on its latest legal tussle with Apple. In this new…