This controls how long Squid waits to declare a peer cache
as "dead." If there are no ICP replies received in this
amount of time, Squid will declare the peer dead and not
expect to receive any further ICP replies. However, it
continues to send ICP queries, and will mark the peer as
alive upon receipt of the first subsequent ICP reply.
This timeout also affects when Squid expects to receive ICP
replies from peers. If more than 'dead_peer' seconds have
passed since the last ICP reply was received, Squid will not
expect to receive an ICP reply on the next query. Thus, if
your time between requests is greater than this timeout, you
will see a lot of requests sent DIRECT to origin servers
instead of to your parents.