TLS 1.3 and DTLS 1.2 + CID hide the real content type of a record
within the record's inner plaintext, while always using the same
content type for the protected record:
- TLS 1.3 always uses ApplicationData
- DTLS 1.2 + CID always uses a special CID content type.
This commit enhances the record encryption unit test to check
that the record content type is indeed correctly hidden.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>