Set an independent thread_data_used for each thread group instead of sharing one thread_data_used

"thread_data_used" indicate the usage of EThread::thread_private[ ].

The EThread::thread_private[ ] saved thread specific data e.g. :

• stat system arrays
• NetHandler object
• PollCont object

However, the private data of thread group are different.

Sharing thread_data_used cause the waste of space.