Revert ed82eb2702d0 on wifi/model/wifi-mad-header.cc to diagnose valgrind error.

src/wifi/model/wifi-mac-header.cc

@@ -884,11 +884,9 @@ WifiMacHeader::GetSize (void) const
 const char *
 WifiMacHeader::GetTypeString (void) const
 {
-  std::string typeString;
-  
 #define FOO(x) \
 case WIFI_MAC_ ## x: \
-  typeString = # x; \
+  return # x; \
   break;
 
   switch (GetType ())
@@ -932,7 +930,8 @@ case WIFI_MAC_ ## x: \
       return "ERROR";
     }
 #undef FOO
-  return typeString.c_str ();
+  // needed to make gcc 4.0.1 ppc darwin happy.
+  return "BIG_ERROR";
 }
 
 TypeId