- refs #10646 where reuse was attempted on closed connections in the
cache, leading to an exhaustion of retries on a transfer
- the mistake was that poll events like POLLHUP, POLLERR, etc
were regarded as "not dead".
- change cf-socket filter check to regard such events as inidication
of corpsiness.
- vtls filter checks: fixed interpretation of backend check result
when inconclusive to interrogate status further down the filter
chain.
Reported-by: SendSonS on github
Fixes#10646Closes#10652