Refactor the LinkDiscovery and fix the dropping of portDesc

Refactor the LinkDiscovery that to use the DeviceId instead of Device.
And fix the issue that using of portDesc is dropped in getLinkProbe.

ONOS-7834

Change-Id: I5af1bbb2207b607555bc41ea480a599e1d092a14
diff --git a/providers/lldp/src/main/java/org/onosproject/provider/lldp/impl/LldpLinkProvider.java b/providers/lldp/src/main/java/org/onosproject/provider/lldp/impl/LldpLinkProvider.java
index 8be22f9..e2d45a5 100644
--- a/providers/lldp/src/main/java/org/onosproject/provider/lldp/impl/LldpLinkProvider.java
+++ b/providers/lldp/src/main/java/org/onosproject/provider/lldp/impl/LldpLinkProvider.java
@@ -451,7 +451,7 @@
         }
 
         LinkDiscovery ld = discoverers.computeIfAbsent(device.id(),
-                                     did -> new LinkDiscovery(device, context));
+                                     did -> new LinkDiscovery(device.id(), context));
         if (ld.isStopped()) {
             ld.start();
         }