DDSSEC12 — CryptoTransformIdentifier extensibility FINAL is not compatibly with its derived classes

Section 7.3.7.3 defines CryptoHeader as inheriting from CryptoTransformIdentifier. However CryptoHeader is APPENDABLE and CryptoTransformIdentifier is FINAL.

This does not seem possible according to XTYPES.

Other places of the spec (section 9.5.2.3 "DDS:Crypto:AES-GCM-GMAC CryptoHeader") define it as final.

Change CryptoHeader definition in 7.3.7.3. to final

In section 7.3.7.3 "Mapping of the CryptoHeader SubmessageElement"
modify the extensibility of CryptoHeader from "APPENDABLE" to "FINAL" resulting in the following IDL:

@extensibility(FINAL)
struct CryptoHeader : CryptoTransformIdentifier  {
    // Extra plugin-specific information added below
    // PluginHeader   plugin_crypto_header_extra;
};