ONOS-1440: Implements port statistics feature, which polls port statistics of all devices every 10 seconds. Also, implemented a simple portstats ONOS CLI command to show the statistics.

Change-Id: I57e046ae2c2463a58b478d3a5b523422cde71ba2
diff --git a/core/api/src/main/java/org/onosproject/net/device/DeviceProviderService.java b/core/api/src/main/java/org/onosproject/net/device/DeviceProviderService.java
index f48543c..9a1d923 100644
--- a/core/api/src/main/java/org/onosproject/net/device/DeviceProviderService.java
+++ b/core/api/src/main/java/org/onosproject/net/device/DeviceProviderService.java
@@ -19,6 +19,7 @@
 import org.onosproject.net.MastershipRole;
 import org.onosproject.net.provider.ProviderService;
 
+import java.util.Collection;
 import java.util.List;
 
 /**
@@ -70,4 +71,12 @@
      */
     void receivedRoleReply(DeviceId deviceId, MastershipRole requested, MastershipRole response);
 
+    /**
+     * Sends statistics about all ports of a device.
+     *
+     * @param deviceId          identity of the device
+     * @param portStatistics  list of device port statistics
+     */
+    void updatePortStatistics(DeviceId deviceId, Collection<PortStatistics> portStatistics);
+
 }