trace: reimplement the DTRACE function so it doesn't use a vector

At the same time, rename the trace flags to debug flags since they
have broader usage than simply tracing.  This means that
--trace-flags is now --debug-flags and --trace-help is now --debug-help

src/dev/etherlink.cc

@@ -40,6 +40,8 @@
 
 #include "base/random.hh"
 #include "base/trace.hh"
+#include "debug/Ethernet.hh"
+#include "debug/EthernetData.hh"
 #include "dev/etherdump.hh"
 #include "dev/etherint.hh"
 #include "dev/etherlink.hh"