Use more descriptive thread names for worker threads.

In normal operation oscam uses a lot of work_threads. This
commit gives them descriptive names. Previously all threads
were called work_thread.

Unfortunately the thread name can not exceed 16 characters,
so we can not be very descriptive.

git-svn-id: http://streamboard.de.vu/svn/oscam/trunk@8297 4b0bc96b-bc66-0410-9d44-ebda105a78c1