[ONOS-8087] Per device purgeOnDisconnection Flag

Change-Id: I7cb1db12a4d910d70123f116107a898bf9e6d278
diff --git a/app/src/main/java/org/onosproject/segmentrouting/config/DeviceConfiguration.java b/app/src/main/java/org/onosproject/segmentrouting/config/DeviceConfiguration.java
index 123da37..5013e83 100644
--- a/app/src/main/java/org/onosproject/segmentrouting/config/DeviceConfiguration.java
+++ b/app/src/main/java/org/onosproject/segmentrouting/config/DeviceConfiguration.java
@@ -35,6 +35,7 @@
 import org.onosproject.net.HostId;
 import org.onosproject.net.PortNumber;
 import org.onosproject.net.config.ConfigException;
+import org.onosproject.net.config.basics.BasicDeviceConfig;
 import org.onosproject.net.config.basics.InterfaceConfig;
 import org.onosproject.net.host.InterfaceIpAddress;
 import org.onosproject.net.intf.Interface;
@@ -109,6 +110,12 @@
         Set<DeviceId> deviceSubjects =
                 srManager.cfgService.getSubjects(DeviceId.class, SegmentRoutingDeviceConfig.class);
         deviceSubjects.forEach(subject -> {
+            //Setting purge on disconnection flag for the device SR has control over.
+            // addConfig returns a config if it exists or creates a new one.
+            log.info("PurgeOnDisconnection set to true for device {}", subject);
+            BasicDeviceConfig basicDeviceConfig = srManager.cfgService.addConfig(subject, BasicDeviceConfig.class);
+            basicDeviceConfig.purgeOnDisconnection(true);
+            srManager.cfgService.applyConfig(subject, BasicDeviceConfig.class, basicDeviceConfig.node());
             SegmentRoutingDeviceConfig config =
                     srManager.cfgService.getConfig(subject, SegmentRoutingDeviceConfig.class);
             SegmentRouterInfo info = new SegmentRouterInfo();