vehicle-aidl: Fix various race condition

mThread should not be created in initization list,
since class member variables are not ready yet,
and the thread will access those variables.

Even if the shared variable is atomic, it must be modified under the
mutex in order to correctly publish the modification to the waiting
thread.

Bug: 231668271
Test: android.hardware.automotive.vehicle@V1-default-service_fuzzer
Change-Id: Ibbf36ddf9edcaa8d016349631784f54f6fd6c877