This patch adds packet tracing to the communication monitor using a
protobuf as the mechanism for creating the trace.
If no file is specified, then the tracing is disabled. If a file is
specified, then for every packet that is successfully sent, a protobuf
message is serialized to the file.
This patch adds a basic regression for the traffic generator. The
regression also serves as an example of the file formats used. More
complex regressions that make use of a DRAM controller model will
follow shortly.