That would not be possible on a secured android device, ie, it is off topic
for this group

The code has been built to be a .so by NDK.

The code to be run as root must be a stand alone executable rather than a
jni library, so it can run in a new process.  The "su" hack on some
unofficial roms does not and can not be made to elevate an application to
root, all it can do is launch a new process from a stand alone executable
and have that process run as root and perhaps do things on behalf of your
app.

It's not really on topic here as its outside of the capabilities of the
android sdk but it's been covered numerous times on stack overflow.