Test that Shutdown does not surface closed errors (#624)
Test that Shutdown does not surface closed errors (#624)

* Test that Shutdown does not surface closed errors

This test checks that calling Shutdown does not cause ActivateAndServe
(via serveTCP and serveUDP) to return the underlying
'use of closed network connection' error.

This commit unifies TestShutdownTCP with TestShutdownUDP. After this
commit, both tests will check that ActivateAndServe returns a nil error
and that Shutdown succeeded.

This was previously broken for serveTCP.

* Add comment explaining why fin chan is buffered

miekg/dns