Use the local context on Impl to check for shut down state in order to
drop rather than inject packets after close has begun.
Netstack sets endpoint.dispatcher to nil during shutdown. After the
recent adjustment in 920ec69241 we now
wait for netstack to fully shutdown before we release tests. This means
that we may continue to accept packets and attempt to inject them, which
we must prevent in order to avoid nil pointer panic.
References google/gvisor#8765Fixes#7715
Signed-off-by: James Tucker <james@tailscale.com>
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