Fix HDP select thread id type

Recent changes in libbionic cause pthread_join to SIGABRT if called with
an invalid thread id. The select_thread_id variable in the HDP
sub-system was truncated from long->int causing pthread_join to not find
the correct thread and triggering the error.

Using the correct type for select_thread_id fixes this problem.

Change-Id: Id332fa86cf7f30abd211588d32899d41e157b462
Fixes: 35432169
Test: manual; boot device, turn BT off; ensure it stays off