Accept a new connection.

template<
    typename Protocol1,
    typename SocketService>
asio::error_code accept(
    implementation_type & impl,
    basic_socket< Protocol1, SocketService > & peer,
    endpoint_type * peer_endpoint,
    asio::error_code & ec,
    typename enable_if< is_convertible< Protocol, Protocol1 >::value >::type *  = 0);