Complete QUIC MUX timeout refresh function by using http-keep-alive timeout. It is used when the connection is idle after having handle at least one request. To implement this a new member <idle_start> has been defined in qcc structure. This is used as timestamp for when the connection became idle and is used as base time for http keep-alive timeout (cherry picked from commit bd6ec1bf845736d7447669077b4f3f2c4bd48011) Signed-off-by: Willy Tarreau <w@1wt.eu>