BUG/MINOR: mux_quic: make sure to always apply offsets to now_ms in expiration

BUG/MINOR: mux_quic: make sure to always apply offsets to now_ms in expiration

Now_ms can be zero nowadays, so it's not suitable for direct assignment to
t->expire, as there's a risk that the timer never wakes up once assigned
(TICK_ETERNITY). Let's use tick_add(now_ms, 0) for an immediate wakeup
instead. The impact looks nul since the task is also woken up, but better
not leave such tasks in the timer tree anyway.

This should be backported where it applies.