Fix compatibility with python3.6+

[DL6ER]

Fixes compatibility with python3.6+ (tested with Ubuntu python3.8.1). More details directly in the fixed code.

@sibbi77 mentioned incompatibility with python3.6 in https://github.com/Robpol86/libnl/issues/28 If you're still interested, could you verify my patch fixes the issue also for you?

My patch should be python2.6 compatible.

Side note: You mentioned in said issue that you stopped maintaining the project. As I'm planing to use it in future projects, I'd volunteer to make it over if you want this. It would both make my life easier and ensure this project will live on with new developments and fixes (where needed).

[sibbi77]

Import works now (python 3.8). I did no further tests on this. vy 73 DH9SH