In PR #66, we tried to address a memory leak by avoiding
runtime.SetFinalizer for autodrainingInboundQueue and
autodrainingOutboundQueue unless there was something to do.
However, when there is work to be done, these finalizers still leak
memory because they’re still holding on to a cyclical reference to q.
This applies to any platform that relies on a bounded device.WaitPool,
like Android and iOS which both declare PreallocatedBuffersPerPool.
This patch converts this logic to runtime.AddCleanup which is designed
to avoid this problem.
Updates tailscale/corp#42776
Signed-off-by: Simon Law <sfllaw@tailscale.com>
cd7ac13b86