Benchmark Sniffnet performance

This issue wants to track the need for a benchmark to accurately measure the speed of the app, measured in packets per second (pps) that can be handled without dropping frames.

This is necessary to find out ways that can help improving the performance even further.

> Today I tried testing Sniffnet with `iperf` on a different machine and I could observe that the current packets per second limit is higher than 100k:
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> _Originally discussed in #373_

Start by reviewing the Sniffnet packet-capture path and the prior discussion in #373, then reproduce the existing iperf observation. Define a repeatable benchmark that measures packets per second without dropped frames; done means the benchmark can report those results consistently and help compare performance changes.

Written by the indexing model from the issue text.