Webservice: Default to IPv6 compatible binds

What does this MR do?

Webservice: Default to IPv6 compatible binds

We disabled IPv6 compatible binds in !4382 (merged) because of a issue with throttling of unauthenticated web traffic.

Now with gitlab-org/gitlab!196981 (merged) rails should see the real client IP, even if the client or one of the intermediate proxies was mapped to an IPv6 address, so we can default to IPv6 compatible binds.

Related issues

Closes Webservice: Enabling IPv6 breaks unauthenticate... (#6084)

Relates Deployment in a complete IPv6 only environment (#2778 - closed)

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Closes #6084