[nginx-quic] fix qpack index issue when lookingup dynamic table

[Sergey Kandaurov]

> On 24 May 2021, at 06:34, sun edward <sunzhiyong3210 at gmail.com> wrote:
> 
> description:
>      when qpack header insert with name reference, if it is dynamic table, the index should be the relative index, as described in drafts:
> https://quicwg.org/base-drafts/draft-ietf-quic-qpack.html#name-insert-with-name-reference 

Committed, thanks.
https://hg.nginx.org/nginx-quic/rev/e6c26cb4d38b

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-- 
Sergey Kandaurov