Move queue management into mbedtls_test_ssl_dtls_join_endpoints

This allows mbedtls_test_ssl_endpoint_init() to no longer interact with the
other endpoint.

No behavior change.

Signed-off-by: Gilles Peskine <[email protected]>

tests/include/test/ssl_helpers.h

@@ -205,6 +205,7 @@ typedef struct mbedtls_test_ssl_endpoint {
 
     /* Objects owned by the endpoint */
     int *ciphersuites;
+    mbedtls_test_ssl_message_queue queue_input;
     mbedtls_x509_crt *ca_chain;
     mbedtls_x509_crt *cert;
     mbedtls_pk_context *pkey;