server_queuereader: make comments less misleading
server_queuereader: only disconnect idle TCP connections

It makes little to no sense to disconnect our internal pipes, or UDP
connections for reasons of being idle, since we know we will use them
(pipes) or because they are not connected (UDP).
server_queuereader: suppress fail/recovery messages for UDP

Since we cannot reliably say anything about the state of an UDP
connection, just be quiet about it.  UDP is unreliable, so if it fails,
that's just nothing new.  If it doesn't fail for us, it can still fail
on another level.