dos: Limit connections by IP prefix

Created by: dagurval

Mitigation against one actor using all connection slots.

The choice of using IP prefix was out of simplicity. This is probably not a great way to segregate connections.

Limitations: Because of the way websockets are implemented, this is effectively also a global limit for websocket connections.

Test plan

Unit test added for this feature.

cargo test ./contrib/run_functional_tests.py