Return PRECONDITION_NOT_MET if security not supported

As opposed to NOT_ALLOWED_BY_SECURITY.  There is a meaningful
difference between something being disallowed and something being
impossible.

Co-Authored-By: Kyle Fazzari <github@status.e4ward.com>
Signed-off-by: Erik Boasson <eb@ilities.com>

src/core/ddsc/include/dds/dds.h

@@ -739,8 +739,22 @@ dds_set_listener(dds_entity_t entity, const dds_listener_t * listener);
  *
  * @retval >0
  *             A valid participant handle.
+ * @retval DDS_RETCODE_NOT_ALLOWED_BY_SECURITY
+ *             An invalid DDS Security configuration was specified (whether
+ *             that be missing or incorrect entries, expired certificates,
+ *             or anything else related to the security settings and
+ *             implementation).
+ * @retval DDS_RETCODE_PRECONDITION_NOT_MET
+ *             Some security properties specified in the QoS, but the Cyclone
+ *             build does not include support for DDS Security.
+ * @retval DDS_RETCODE_OUT_OF_RESOURCES
+ *             Some resource limit (maximum participants, memory, handles,
+ *             &c.) prevented creation of the participant.
  * @retval DDS_RETCODE_ERROR
- *             An internal error has occurred.
+ *             The "CYCLONEDDS_URI" environment variable lists non-existent
+ *             or invalid configuration files, or contains invalid embedded
+ *             configuration items; or an unspecified internal error has
+ *             occurred.
  */
 DDS_EXPORT dds_entity_t
 dds_create_participant(

src/core/ddsi/src/q_entity.c

@@ -966,7 +966,7 @@ dds_return_t new_participant_guid (ddsi_guid_t *ppguid, struct ddsi_domaingv *gv
   {
     /* disallow creating a participant with a security configuration if there is support for security
        has been left out */
-    ret = DDS_RETCODE_NOT_ALLOWED_BY_SECURITY;
+    ret = DDS_RETCODE_PRECONDITION_NOT_MET;
     goto not_allowed;
   }
 #endif