Description
This ticket was split from SPDY ticket(TS-2431), and it relys on the patch of TS-2612.
Add "client_protocol_stack"(%<cps>) field into LogFormat.
The Client Protocol Stack is usually composed by transport protocol(UDP, TCP, TLS, ...) and application protocol(HTTP, SPDY, RTMP, WebSocket, ...).
The output of %<cps> field would be the conjunction of protocol names in client protocol stack spliced with '+', such as
"HTTP" // "TCP" is the defualt transport protocol, would be omitted by default. "TLS+SPDY" "TLS+HTTP"