HTTP CONNECT: handle early server packets

[mjameswh]

When using an HTTP CONNECT proxy, it is possible for the server's first HTTP2 packet to reach the client before the node's HTTP library even starts parsing the HTTP HTTP/1.1 200 Connected response.

When that happens, node's HTTP response parser may take these extra bytes (i.e. the server's first HTTP2 packets) out of the socket into its parsing buffer. That means that these extra bytes will not be emitted through the tunneled socket provided on the connect event. Instead, these extra bytes are provided through the head parameter of the connect event.

This PR reinjects these extra bytes (if any) into the tunneled socket.

Fixes #2744.

[linux-foundation-easycla]

• ❌ - login: @mjameswh / name: James Watkins-Harvey . The commit (3e89fdc) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

[murgatroid99]

This change looks good, but I can't merge it until you sign the CLA.

[mjameswh]

I know. I'm waiting for legal department.