message: mavsdk_server: use default port 50051
  It was not very intuitive if the server does not work when you start it
  without an optional argument. I prefer this way where the default is
  sane and gets you started.
diff: #include <string>
  static auto constexpr default_connection = "udp://:14540";
  -static auto default_mavsdk_server_port = 0;
  +static auto constexpr default_mavsdk_server_port = 50051;
  static void usage(const char* bin_name);
  static bool is_integer(const std::string& tested_integer);
  @@ -59,7 +59,8 @@ void usage(const char* bin_name)
  << '\n'
  << "Options:" << '\n'
  << " -h | --help : show this help" << '\n'
  - << " -p : set the port on which to run the gRPC server" << '\n';
  + << " -p : set the port on which to run the gRPC server\n"
  + << " (default is " << default_mavsdk_server_port << ")\n";
  }
  bool is_integer(const std::string& tested_integer)
  