Function soup_sys::soup_session_send_async

pub unsafe extern "C" fn soup_session_send_async(
    session: *mut SoupSession, 
    msg: *mut SoupMessage, 
    cancellable: *mut GCancellable, 
    callback: GAsyncReadyCallback, 
    user_data: gpointer
)

This is supported on crate feature v2_42 only.