- Enable the commented out locking in fd_probe(). The worker thread
should not be running yet (even after these changes), but better to be
safe than sorry.
- Defer starting the worker thread until after the child drives have been
probed. The worker thread startup is moved into a fdc_start_worker()
thread that the various front ends call at the end of attach. As a
side effect this fixes a few edge cases that weren't shutting down the
worker thread if attach encountered a late failure.
- When executing the initial reset requested by attach in the worker
thread, use DELAY() instead of a tsleep() if cold is set.
Tested by: Howard Su <howard0su@gmail.com>
Sponsored by: Netflix
