Function sd_bus_call_async 

pub unsafe extern "C" fn sd_bus_call_async(
    bus: *mut sd_bus,
    slot: *mut *mut sd_bus_slot,
    m: *mut sd_bus_message,
    callback: sd_bus_message_handler_t,
    userdata: *mut c_void,
    usec: u64,
) -> c_int