standalone snowflake operators want a way to bind a specific outbound address

This is similar to Tor's OutboundBindAddress config option: if you're running headless snowflake on a server with multiple IP addresses, you want a way to control which IP address your outgoing connections will come from.

Tricks can be done with routing and iptables and etc, but those are OS-specific, require messing with stuff at the root level, etc. Maybe it is a two-line patch to let snowflake call bind() on the outbound connection socket?