Support sni_hostname extension with SOCKS proxy

[Allgot]

• Support sni_hostname extension with SOCKS proxy.

• This is a complementary update of Add sni hostname extension #696.

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Co-authored-by: Tom Christie tom@tomchristie.com

Summary

A new extension, sni_hostname has enalbed users to specify the hostname which would be used during TLS handshake. However, the update was inconsistent, resulting in the incomplete extension. Currently, the sni_hostname extension are not handled if SOCKS proxy is in use. This PR would bridge this gap.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[Allgot]

Sorry for the confusing PR. I created a new branch from the HEAD by mistake.

I would close this PR right now, then create new one properly. Sorry.