Fix: Address a few benign memory leaks

This patch is the result of static analysis identifying a number of
memory leaks. The leaks are all benign as they are a result of not
deallocating memory in the desctructor. The fix still has value as it
removes false positives in the static analysis.

src/dev/ethertap.cc

@@ -147,6 +147,7 @@ EtherTap::~EtherTap()
     if (buffer)
         delete [] buffer;
 
+    delete interface;
     delete listener;
 }