Overhaul bench

[aochagavia]

This PR introduces a few options to benchmark more effectively:

• Disable encryption (using the --no-protection flag, similar to the perf crate).
• Run on a simulated in-memory network, instead of going through the networking stack of the operating system (using the --simulate-network together with the --simulated-link-latency and --simulated-link-capacity options). This makes it trivial to benchmark for different latencies and link capacities out-of-the-box (instead of relying on platform-specific utilities like tc).
• Disable MTUD (using --disable-mtud) and set the minimum MTU (using --min-mtu), to make runs more deterministic

[aochagavia]

Closing this, since there is little chance I'll be able to work on it anytime soon