Account for additional record expansion when using CIDs

Using the Connection ID extension increases the maximum record expansion
because
- the real record content type is added to the plaintext
- the plaintext may be padded with an arbitrary number of
  zero bytes, in order to prevent leakage of information
  through package length analysis. Currently, we always
  pad the plaintext in a minimal way so that its length
  is a multiple of 16 Bytes.

This commit adapts the various parts of the library to account
for that additional source of record expansion.

library/ssl_tls.c

@@ -9261,6 +9261,11 @@ int mbedtls_ssl_get_record_expansion( const mbedtls_ssl_context *ssl )
             return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
     }
 
+#if defined(MBEDTLS_SSL_CID)
+    if( transform->out_cid_len != 0 )
+        transform_expansion += MBEDTLS_SSL_MAX_CID_EXPANSION;
+#endif /* MBEDTLS_SSL_CID */
+
     return( (int)( out_hdr_len + transform_expansion ) );
 }