MINOR: mux-quic: hide traces when woken up on pacing only

MINOR: mux-quic: hide traces when woken up on pacing only

Previous commit aligned default and pacing emission. This is a cleaner
and more robust code. However, it may disrupt traces analysis when
pacing is rescheduled until timer expiration.

Hide traces when qcc_io_cb() is woken up only due to pacing and timer is
not yet expired. This is implemented by using special TASK_WOKEN_IO for
pacing.

This should be backported up to 3.1.

(cherry picked from commit 53db43aff231d83ea6f6bcaf99f5bdb5a0330e7b)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>