Add [features] section to .cfg:

This non-production config section allows features to be enabled
by listing their text descriptions, one line each, in the config
section titled "features".

NOTE: Feature names with leading or trailing whitespace, or
      containing an equals sign ('=') are not supported.

src/ripple/app/tx/impl/apply.cpp

@@ -86,8 +86,8 @@ preflight (Rules const& rules, STTx const& tx,
 {
     try
     {
-        PreflightContext pfctx(
-            tx, rules, flags, verify, j);
+        PreflightContext pfctx(tx,
+            rules, flags, verify, config, j);
         return invoke_preflight(pfctx);
     }
     catch (std::exception const& e)