Update scan.c

Hello,

thank you very much for the great work on openDIAS. I really appreciate how you get such a good application out of such a little piece of code.

I installed your ubuntu 14.04 package today to use it on my synology diskstation. My setup includes a sane backend installed using the diskstations ipkg system and openDIAS installed in a chroot environment built up on Ubuntu 14.04. Everything installed fine in the first place using your deb files. However, I did not manage to access the scanner using the sane net backend. Doing a little research I found out, you were only scanning for devices attached locally. I changed that in the code (probably that could also be an option for the user), so now also net devices are returned when calling sane_get_devices.

I hope this change does not destroy any intentions you had with your original code.

Thanks again for your great work!

Kind regards,
Michael

P.S. I created an ubuntu amd64 package including the change. However I really did a lot of trial and error until I got there. So I'm not sure the quality of the deb meets your expectations. If you think it could please give me a hint, so I can put it somewhere for download.