Remove 'tcpip6' service dependency for Vista and above 

Hello Tomek.

This is my first pull request ever. I tried one year ago to use Dibbler in Windows 7 and now I decided to use in Windows 8. I thought that this problem would be solved by then, but it seems that the majority of dibbler users are *nix users . I've searched the internet and there are very few people complaining about Dibbler being unable to start after it is installed as a Service in Windows because the tcpip6 service fails to start on Windows Vista and above.

TSrvService ctor now detects the running version of windows at runtime. The dependency on the 'tcpip6' service should only exist if Dibbler is running in Windows XP or Windows 2003.