Function safe_app::ffi::immutable_data::idata_size

#[no_mangle]
pub unsafe extern "C" fn idata_size(
    app: *const App, 
    se_h: SEReaderHandle, 
    user_data: *mut c_void, 
    o_cb: extern "C" fn(user_data: *mut c_void, result: *const FfiResult, size: u64)
)

Get data size from Self Encryptor.

Callback parameters: user data, error code, size