Construct a basic_datagram_socket without opening it.

basic_datagram_socket(
    asio::io_service & io_service);

basic_datagram_socket(
    asio::io_service & io_service,
    const protocol_type & protocol);

basic_datagram_socket(
    asio::io_service & io_service,
    const endpoint_type & endpoint);

basic_datagram_socket(
    asio::io_service & io_service,
    const protocol_type & protocol,
    const native_type & native_socket);