Support for client metadata at regular intervals.

[kylemallory]

I am fairly new to iperf (I'm familiar with it, but haven't used it regularly in the past). Recently, I am wanting to profile bandwidth to our iperf server (across a LAN) from various points on our campus, connected via WIFI, and in "real time", while walking between indoor/outdoor areas, etc.
I would like to propose that the client be able to transmit, in chunks at regular, configurable intervals (probably between blocks), a JSON payload of metadata that would be received by the server, and logged along with the performance results. This data could provide a standard set of parameters such as a timestamp, the client & server IP, ports, device info, etc, but could also be expanded by the client application to include device name, OS, GPS coordinates, WiFi signal strength, etc -- obviously, these would need extensions or custom clients to leverage completely, but at the least, the CLI client could have command args to include some of this data.