trace: support HTTP/1.1 chunked encoding

[Achille]

Our implementation of message tracing for HTTP currently breaks when the request or response does not contain a Content-Length header, but boundaries of messages in HTTP/1.1 may be defined by using the Transfer-Encoding header, or simply by closing the TCP stream.

We should have complete support for the HTTP/1.1 protocol to support tracing a wide range of applications.