dvbapi: Check at least 8 adapters when detecting api.

Allow dvbapi to detect API version even if /dev/dvb/adapter0 is unavailable.

Original comments from the patch author:

> I have removed one (dual tuner) adapter from my pc. Since I use fixed
> adapter numbers, I ended up with:
> /dev/dvb/adapter2
> /dev/dvb/adapter3
>
> Then dvbapi stopped working because when detecting the api, it was only
> search for /dev/dvb/adapter0
>
> This patch make the detection search at least the presence of 8 adapters.
> (tested and working)

From: Luis Alves <ljalvs@gmail.com>

This contains fix for ticket #3489.

git-svn-id: http://streamboard.de.vu/svn/oscam/trunk@8995 4b0bc96b-bc66-0410-9d44-ebda105a78c1