Provide ability to round robin outgoing exit connections on multiple interfaces
Multithreading support may improve our ability to support high-throughput multicore tor nodes, but it is not the whole story. To avoid TCP source port exhaustion on high capacity exit relays, we will need the ability to support multiple interfaces for outgoing exit connections.
To minimize stupid website breakage, we probably want to keep every connection from the same circuit on the same interface, but round robin circuits across different outgoing interfaces.