Linux Upload Throughput Perf is Bimodal

[nibanks]

Describe the bug

Ever since we added GSO support Linux (on Ubuntu 20.04) single connection upload throughput performance tests have produced bimodal results (dashboard link). It oscillates between 4.8 Gbps and 2.8 Gbps. We haven't spent any time investigating. Most of our existing tools (using WPA to analyze traces) don't yet work with LTTng, so either some other means would need to be used or the tooling needs to add support.