fix_issue_350_gtpu_init

Fix issue 350 Fix hidden bug in new itti (in a not yet used function) Add signal handler for SIGINT for record I/Q feature, it also calls the UHD close function: may help to leave USRP in good status Some code re-organization to improve code readability and to use later a different threading model: S1AP, SCTP, ... main loop separated in two functions: init and process message (as it was already in gtpu for example)