enable nsc when nsc enabled

src/internet-stack/wscript

@@ -75,7 +75,7 @@ def configure(conf):
     ok = False
     if arch == 'x86_64' or arch == 'i686' or arch == 'i586' or arch == 'i486' or arch == 'i386':
         conf.env['NSC_ENABLED'] = 'yes'
-        conf.define('NETWORK_SIMULATION_CRADLE', 1)
+        conf.env.append_value('CXXDEFINES', 'NETWORK_SIMULATION_CRADLE')
         e = conf.create_library_configurator()
         e.mandatory = True
         e.name = 'dl'