Update api-ref for set registered limits.

The help messages are updated for set registered
limit [1]. Document is also updated for the same.

[1] https://review.openstack.org/#/c/609985/

Change-Id: I48ab54b909e6758f61aa95c9d96f727689ad767a

api-ref/source/v3/parameters.yaml

@@ -1573,6 +1573,14 @@ request_default_limit_body_not_required:
   in: body
   required: false
   type: integer
+request_region_id_registered_limit_body_not_required:
+  description: |
+    The ID of the region that contains the service endpoint.
+    Either service_id, resource_name, or region_id must be
+    different than existing value otherwise it will raise 409.
+  in: body
+  required: false
+  type: string
 request_resource_limit_body_not_required:
   description: |
     The override limit.
@@ -1581,16 +1589,18 @@ request_resource_limit_body_not_required:
   type: integer
 request_resource_name_body_not_required:
   description: |
-    The resource name.Either service_id or resource_name must be
-    different than existing value otherwise it will raise 409.
+    The resource name. Either service_id, resource_name or
+    region_id must be different than existing value otherwise
+    it will raise 409.
   in: body
   required: false
   type: string
 request_service_id_registered_limit_body_not_required:
   description: |
     The UUID of the service to update to which the registered
-    limit belongs. Either service_id or resource_name must be
-    different than existing value otherwise it will raise 409.
+    limit belongs. Either service_id, resource_name, or region_id
+    must be different than existing value otherwise it will
+    raise 409.
   in: body
   required: false
   type: string

api-ref/source/v3/unified_limits.inc

@@ -163,7 +163,7 @@ Parameters
    - registered_limit_id: registered_limit_id_path
    - registered_limit: registered_limit
    - service_id: request_service_id_registered_limit_body_not_required
-   - region_id: region_id_request_body
+   - region_id: request_region_id_registered_limit_body_not_required
    - resource_name: request_resource_name_body_not_required
    - default_limit: request_default_limit_body_not_required
    - description: description_registered_limit_request_body