Pre-work for pause: Virtual Input Queue,
matches up with DropTail on simpleDCTCPDumbbell.tcl
Make all queues in the network VirtualInputQueues for pause
Utility function to get total input port occupancy across all outputs
Utility function for pointer chasing across connectors
Classifier now includes a node id to track input port for viq
Add input port field to packet, set it using Classifier's node_id_
Track input occupancy across all outputs for pause