[Docker-outside-of-docker] Increase backlog depth for socat proxy (#789)

[groner]

The underlying problem described in #789 is that the main accept(2) loop in socat is single threaded and is easily overwhelmed by docker compose, which can create connection attempts in multiple cores.

Fortunately the listening socket already has a backlog which we can increase from socat's default of 5.

In this PR I have chosen a depth of 128 as probably high enough for most devcontainer needs. If it isn't high enough this could be made tunable, but reevaluating the proxy implementation might be in order also.

[eljog]

Thank you for the contribution.
I can approve to run the pipeline checks once the CLA has been accepted

Also, please consider adding more context and details to the PR description

[groner]

@microsoft-github-policy-service agree

[groner]

@eljog Thanks for looking at this.

I've added some details to the description, but refer to #789 for context. I hope that's alright.

[eljog]

I have approved to run the workflow checks