Are there other things we might want to tweak using socket2? The only thing I'm hesitating about is the name of the keepalive since we might want one more generic tcp-extra or something.

If this lands in std::net eventually, we can make the feature flags a no-op, but it'd be nice to not have many many flags in that case.

I think tcp-extra or socket-opts is a better feature flag name as I can see support for setting TCP_NODELAY being useful, especially since ureq seems to write requests in a way that is known to occassionally cause issues when Nagle's algorithm is on the client and delayed acknowledgements are used on the server (writing header and body in two separate calls).

EDIT:
I see TCP_NODELAY is already possible to set. Similar logic applies for wanting to set TCP_QUICKACK and others.