Set "input_port()" on deque from last hop
Change input_port and key in input_counters_ to int32_t
to allow negative keys (corresponds to an Agent port on a host node)
Set input port of -1 on endhost agents as well.
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
Prep for pause: Measure input occupancy in DestHashClassifier::recv()