Revert "Implement 'record-only' mode, where messages are received but not sent to the network."

This reverts commit 67cbe4ad6a8b4cc311e59d446b442f418b9c1e57.

Conflicts:
	sts/openflow_buffer.py
REvert to using pass-through rather than record-only. REalized that we need to
fork() rather than record-only, since switches need to respond to messages.