Update In-memory structure for Switch/Port/Link

Change-Id: Ibcdc6ad326016c16f286ce20acd172a93f66adbb
diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/PortImpl.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/PortImpl.java
index 412113c..eb411f0 100644
--- a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/PortImpl.java
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/PortImpl.java
@@ -95,6 +95,10 @@
 	    return this.devices.remove(d);
 	}
 
+	public void removeAllDevice() {
+	    this.devices.clear();
+	}
+
 	@Override
 	public String toString() {
 		return String.format("%d:%d",