adjust http max idle connections per host

related to https://github.com/chrislusf/seaweedfs/issues/1802

weed/operation/upload_content.go

@@ -58,6 +58,7 @@ var (
 
 func init() {
 	HttpClient = &http.Client{Transport: &http.Transport{
+		MaxIdleConns:        1024,
 		MaxIdleConnsPerHost: 1024,
 	}}
 }