Topology manager writes link information everytime topology-lldp-discovery publish the linkAdded/linkRemove notificaiton

In the current implementation of the TopologyManager, it's listening for linkAdded and linkRemoved notification and whenever it receive those notification, it updates the data store. linkAdded and linkRemoved notificaitons are published by topology-lldp-discovery module. Topology-lldp-discovery module will publish this whenever it will receive the lldp packet from the switch. This is not a right behavior, because it's publishing the same linkAdded event everytime it receives the lldp packet. This can cause performance issue when topology is large.

Topology-lldp-discovery module should only publish the linkAdded notification if the link is added first time or removed and added back.