mem: Edit proto Packet and enhance the python script

mem: Edit proto Packet and enhance the python script

This patch changes the decode script to output the optional fields of
the proto message Packet, namely id and flags. The flags field is set
by the communication monitor.

The id field is useful for CPU trace experiments, e.g. linking the
fetch side to decode side. It had to be renamed because it clashes
with a built in python function id() for getting the "identity" of an
object.

This patch also takes a few common function definitions out from the
multiple scripts and adds them to a protolib python module.