Fix no-protection option in perf crate

[aochagavia]

While profiling stuff with perf_server and perf_client, I discovered that the no-protection option was not working as expected (it did not disable packet encryption / decryption, as my flamegraphs revealed). It looks like the original feature did disable encryption after a key update, but forgot to do so right after the handshake. This PR fixes that.

In case you are curious, you can observe the problem by running the following commands:

1. cargo run --release --bin perf_server
2. cargo run --release --bin perf_client -- --no-protection
3. Watch the server and the client happily exchange packets (instead of failing to connect because of the mismatch in encryption)