7 GPUs does not function properly - up to 6 is OK it seems?
I have two systems running on Ubuntu server 16.04, one system with 7 pieces of ASUS 1080Ti and another one with 6 pieces of the same card.

When I execute xmrig-nvidia on the 6 GPU system everything works OK, but on the 7 GPU system it only performs work on 1 card out of 7. I do not think it is donation related, same figures on 7 GPU with 1 and 3% donation.

If I manually specify gpu threads to 6 on this 7 GPU system it detects all cards and runs workloads on them, with reduced performance. 

I have also tried 10,5,4,7 threads but it is quiet random how many cards it runs on when I try something else, sometimes it is 3 cards, next time 2 cards, 6 threads for some reason works best.

Here I run with 6 threads on 7 GPU system in comparison to 6 GPU where I just execute the miner:

![2017-08-31_14-46-44](https://user-images.githubusercontent.com/31510368/29924308-dc14ef46-8e5c-11e7-86ee-b82faf9cb45f.png)
