Change DiscoverSchedulerInterval default value

This patch changes the default value of "DiscoverSchedulerInterval"
from 0 to 30 seconds.

Since Periodic Inquiry is not supported anymore, the option
"DiscoverSchedulerInterval" in main.conf must be updated. As
a first attempt, it was chosen a 30 seconds interval.
diff --git a/src/main.conf b/src/main.conf
index c03f135..8cd132f 100644
--- a/src/main.conf
+++ b/src/main.conf
@@ -27,8 +27,8 @@
 PageTimeout = 8192
 
 # Discover scheduler interval used in Adapter.DiscoverDevices
-# The value is in seconds. Defaults is 0 to use controller scheduler.
-DiscoverSchedulerInterval = 0
+# The value is in seconds. Defaults is 30.
+DiscoverSchedulerInterval = 30
 
 # What value should be assumed for the adapter Powered property when
 # SetProperty(Powered, ...) hasn't been called yet. Defaults to true