[Falcon] link discovery -

- safety checks against fingerprint being null
- checks for foreign fingerprint and probe message origin

Change-Id: I2f3e491802afc2091335bd25fcf24865293bde10
diff --git a/providers/lldp/src/main/java/org/onosproject/provider/lldp/impl/DiscoveryContext.java b/providers/lldp/src/main/java/org/onosproject/provider/lldp/impl/DiscoveryContext.java
index 04729e4..74732ea 100644
--- a/providers/lldp/src/main/java/org/onosproject/provider/lldp/impl/DiscoveryContext.java
+++ b/providers/lldp/src/main/java/org/onosproject/provider/lldp/impl/DiscoveryContext.java
@@ -17,6 +17,7 @@
 
 import org.onosproject.mastership.MastershipService;
 import org.onosproject.net.LinkKey;
+import org.onosproject.net.device.DeviceService;
 import org.onosproject.net.link.LinkProviderService;
 import org.onosproject.net.packet.PacketService;
 
@@ -47,6 +48,13 @@
     PacketService packetService();
 
     /**
+     * Returns the DeviceService reference.
+     *
+     * @return the device service interface
+     */
+    DeviceService deviceService();
+
+    /**
      * Returns the probe rate in millis.
      *
      * @return probe rate