BUG/MINOR: mux-h1: Correctly report Ti timer when HTX and keepalives are used

BUG/MINOR: mux-h1: Correctly report Ti timer when HTX and keepalives are used

When HTTP keepalives are used in conjunction with HTX, the Ti timer
reports the elapsed time since the beginning of the connection instead
of the end of the previous request as stated in the documentation. Th,
Tq and Tt also report incorrectly as a result.

When creating a new h1s, check if it is the first request on the
connection. If not, set the session create times to the current
timestamp rather than the initial session accept timestamp. This makes
the logged timers behave as stated in the documentation.

This fix should be backported to 1.9 and 2.0.