deployment: recommend increasing TCP max window size for multi-region deployents

[nvanbenschoten]

See cockroachdb/cockroach#111238, cockroachdb/cockroach#111241 (comment), and this doc.

Modern linux distributions ship with different default TCP maximum window sizes. We should recommend that users in multi-region deployments increase their default (send and receive) window size to at least 16MB so that they can sustain high throughput communication over high-latency network links.

[rmloveland]

@mdlinville assigning to you as "deployment" but it's coming through KV on-call so let me know

I was thinking this could be added to https://www.cockroachlabs.com/docs/stable/recommended-production-settings#networking (among other places)

[pav-kv]

Putting P-2 since this helps addressing throughput issues we observed in escalations. We mitigated them to a good degree, but properly configuring TCP would be a more systematic fix.