migration: Add postcopy_thread_create()
Postcopy create threads. A common manner is we init a sem and use it to sync
with the thread. Namely, we have fault_thread_sem and listen_thread_sem and
they're only used for this.
Make it a shared infrastructure so it's easier to create yet another thread.
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <
20220301083925.33483-7-peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>