Bump default idleConnsPerHost to control conns in time_wait (#10653)

This PR fixes a hang which occurs quite commonly at higher concurrency
by allowing following changes

- allowing lower connections in time_wait allows faster socket open's
- lower idle connection timeout to ensure that we let kernel
  reclaim the time_wait connections quickly
- increase somaxconn to 4096 instead of 2048 to allow larger tcp
  syn backlogs.

fixes #10413

cmd/http/listen_nix.go

@@ -27,9 +27,9 @@ import (
 var cfg = &tcplisten.Config{
 	DeferAccept: true,
 	FastOpen:    true,
-	// Bump up the soMaxConn value from 128 to 2048 to
+	// Bump up the soMaxConn value from 128 to 4096 to
 	// handle large incoming concurrent requests.
-	Backlog: 2048,
+	Backlog: 4096,
 }
 
 // Unix listener with special TCP options.