clock: Fix MultiClock timeChanged statistic recording subclock signals when warmup-period is set

Same root cause as the CompoundPacketQueueBase statistics: the timeChanged
statistic uses localSignal() to record only the MultiClock's own signal and
ignore the timeChanged signals emitted by its subclocks. When warmup-period
is set, the auto-inserted WarmupPeriodFilter demotes localSignal from the head
of the result-filter chain, making it a no-op, so the subclock signals are
recorded as well.

Set autoWarmupFilter=false and wrap the source in warmup() to keep localSignal
at the head. No effect when warmup-period is 0.

Author: levy

src/inet/clock/model/MultiClock.ned

@@ -45,7 +45,7 @@ module MultiClock extends Module like IClock
         @display("i=block/timer");
         @class(MultiClock);
         @signal[timeChanged](type=simtime_t);
-        @statistic[timeChanged](title="Clock time"; source=localSignal(timeChanged); record=vector; interpolationmode=linear; unit=s);
+        @statistic[timeChanged](title="Clock time"; source=warmup(localSignal(timeChanged)); record=vector; interpolationmode=linear; unit=s; autoWarmupFilter=false);
     submodules:
         clock[numClocks]: <default("SettableClock")> like IClock {
             @display("p=200,200,row,200");