BUG/MINOR: quic: Wrong idle timer expiration (during 20s)

This this commit, this is ->idle_expire of quic_conn struct which must
be taken into an account to display the idel timer task expiration value:

     MEDIUM: quic: Ack delay implementation

Furthermore, this value was always zero until now_ms has wrapped (20 s after
the start time) due to this commit:
     MEDIUM: clock: force internal time to wrap early after boot

Do not rely on the value of now_ms compared to ->idle_expire to display the
difference but use ticks_remain() to compute it.

Must be backported to 2.7 where "show quic" has already been backported.
diff --git a/src/quic_conn.c b/src/quic_conn.c
index 22da207..23e5f28 100644
--- a/src/quic_conn.c
+++ b/src/quic_conn.c
@@ -8358,9 +8358,9 @@
 		else
 			chunk_appendf(&trash, "mux=released                                  ");
 
-		expire = qc->idle_timer_task->expire;
+		expire = qc->idle_expire;
 		chunk_appendf(&trash, "expire=%02ds ",
-		              expire > now_ms ? (expire - now_ms) / 1000 : 0);
+		              TICKS_TO_MS(tick_remain(now_ms, expire)) / 1000);
 
 		chunk_appendf(&trash, "\n");