CAS AIDL: Start thread pool for default service

Add missing call to start the thread pool for the default CAS AIDL
service.

Bug: 301369982
Test: atest android.media.misc.cts.MediaCasTest#testClearKeyApis
Change-Id: I6c0572f8573627a817ac5a429bd6800a95687380
diff --git a/cas/aidl/default/service.cpp b/cas/aidl/default/service.cpp
index bed2f01..076c7bb 100644
--- a/cas/aidl/default/service.cpp
+++ b/cas/aidl/default/service.cpp
@@ -31,6 +31,7 @@
 
 int main() {
     ABinderProcess_setThreadPoolMaxThreadCount(8);
+    ABinderProcess_startThreadPool();
 
     // Setup hwbinder service
     std::shared_ptr<MediaCasService> service = ::ndk::SharedRefBase::make<MediaCasService>();