http2: add SETTINGS_ENABLE_CONNECT_PROTOCOL support

[WeidiDeng]

For golang/go#49918

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Weidi Deng:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Damien Neil:

Patch Set 1:

(2 comments)

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[gopherbot]

This PR (HEAD: 77f622b) has been imported to Gerrit for code review.

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[gopherbot]

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[gopherbot]

This PR (HEAD: bccd6b9) has been imported to Gerrit for code review.

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[gopherbot]

Message from Weidi Deng:

Patch Set 4:

(2 comments)

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[gopherbot]

Message from Damien Neil:

Patch Set 5:

(5 comments)

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[gopherbot]

This PR (HEAD: 4aac677) has been imported to Gerrit for code review.

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[gopherbot]

Message from Weidi Deng:

Patch Set 5:

(5 comments)

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