On a state change, it was possible an aborted probe was pending
finalize. When probe controller is reset, the probe channel
observer was not reset. Create a new non-probe channel observer
on state change to get a fresh start.
Also limit probe finalize wait to 10 seconds max. It is possible
that the estimate is very low and we have sent a bunch of probes.
Calculating wait based on that could lead to finalize waiting for
a long time (could be minutes).
* Simplify probe done handling.
Seeing a case where the channel abserver is not re-created after
an aborted probe. Simplifying probe done (no callbacks, making it
synchronous).
* log more
* Split probe controller from StreamAllocator.
With TWCC, there is a need to check for probe status
in a separate goroutine. So, probe specific stuff need
locking. Split out the probe controller to make that cleaner.
* remove defer
Raja Subramanian