Make etherdump timestamps zero-based.

We previously used the actual wall time for the base timestamps,
making etherdumps non-deterministic.  This fixes that problem and
gets rid of the "malformed packet" at the front that we needed to
provide the right base timestamp to wireshark/tcpdump.

src/dev/etherdump.hh

@@ -51,8 +51,6 @@ class EtherDump : public SimObject
     void dumpPacket(EthPacketPtr &packet);
     void init();
 
-    Tick curtime;
-
   public:
     typedef EtherDumpParams Params;
     EtherDump(const Params *p);