System unable to handle high rate of src mac learning packet-ins

In scale setup, high rate of packet-ins from src mac learning mechanism, can cause queue build up in the notification queue, due to packet punted from all OVSs.

ElanPacketInHandler process the incoming packets in a single thread (the notification thread), which causes delays in handling packets and writing rules back to the OVSs. Meanwhile, traffic keeps flowing in and punted to the controller.

This delay also effects all other types of packets-ins to the controller.