MINOR: log: Add "Tu" timer

MINOR: log: Add "Tu" timer

It can be sometimes useful to measure total time of a request as seen
from an end user, including TCP/TLS negotiation, server response time
and transfer time. "Tt" currently provides something close to that, but
it also takes client idle time into account, which is problematic for
keep-alive requests as idle time can be very long. "Ta" is also not
sufficient as it hides TCP/TLS negotiationtime. To improve that, introduce
a "Tu" timer, without idle time and everything else. It roughly estimates
time spent time spent from user point of view (without DNS resolution
time), assuming network latency is the same in both directions.