MINOR: server: increase the default pool-purge-delay to 5 seconds

The default used to be a very aggressive delay of 1 second before starting
to purge idle connections, but tests show that with bursty traffic it's a
bit short. Let's increase this to 5 seconds.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 074a7ff..d2cdf27 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -12311,7 +12311,7 @@
 pool-purge-delay <delay>
   Sets the delay to start purging idle connections. Each <delay> interval, half
   of the idle connections are closed. 0 means we don't keep any idle connection.
-  The default is 1s.
+  The default is 5s.
 
 port <port>
   Using the "port" parameter, it becomes possible to use a different port to
diff --git a/src/server.c b/src/server.c
index 541dc69..97cc5e0 100644
--- a/src/server.c
+++ b/src/server.c
@@ -1811,7 +1811,7 @@
 	srv->agent.proxy = proxy;
 	srv->xprt  = srv->check.xprt = srv->agent.xprt = xprt_get(XPRT_RAW);
 
-	srv->pool_purge_delay = 1000;
+	srv->pool_purge_delay = 5000;
 	srv->max_idle_conns = -1;
 	srv->max_reuse = -1;