sim: Call regStats of base-class as well

We want to extend the stats of objects hierarchically and thus it is necessary
to register the statistics of the base-class(es), as well.  For now, these are
empty, but generic stats will be added there.

Patch originally provided by Akash Bagdia at ARM Ltd.

src/dev/net/etherdevice.cc

@@ -36,6 +36,8 @@
 void
 EtherDevice::regStats()
 {
+    PciDevice::regStats();
+
     txBytes
         .name(name() + ".txBytes")
         .desc("Bytes Transmitted")