ConnectionManager finally block is blocking and can receive exceptions

[bolt12]

ConnectionManager finally block is blocking and can receive exceptions interrupting important clean connection shutdown.

ConnectionManager's finally block deals with the closing of connections and cancelling their connection handlers. It does so by sequentially traversing the ConnectionManager state, updating and tracing the connections's state and performing a blocking cancel on the connection handler thread.

When working on the connection manager timeout enforcing issue (#3330) it was noticed that one thing that should happen is that if the InboundGovernor dies, the ConnectionManager needs to die as well, otherwise there can be connection in a given state for longer than expected since the InboundGovernor can no longer track the inboundIdleTimeout . Using linkOnly one can make AsyncCancelled exceptions propagate to ConnectionManager thread, however this also means that the ConnectionManager's exception handler might receive sporadic exceptions interrupting the exception handler and abort connection cleanup midway making them timeout later than desired.

To mitigate this one should wrap the block around uninterruptibleMask_