Customizing backlog size

There seems to be no way to customize backlog size of a socket and it is fixed to 128.
https://github.com/envoyproxy/envoy/blob/7ff7cb4c6a1dd62e43ad9aeaee98bb103971ba6a/source/common/network/listener_impl.cc#L52
https://github.com/libevent/libevent/blob/master/listener.c#L180

It would be nice if you can provide an option to change it.