api-ref for inherit trunk segmentation type

This patch updates the api-ref for trunk networking by describing the
applicable values for segmentation_type including the inherit type.

Change-Id: I0772463d71cbb6703345e66f52ad6c02163a00ff
Partial-Bug: #1679999

api-ref/source/v2/parameters.yaml

@@ -5114,7 +5114,17 @@ segmentation_id:
   type: integer
 segmentation_type:
   description: |
-    The segmentation type for the subport.
+    The segmentation type for the subport. Possible values include ``vlan``
+    and ``inherit``. When ``inherit`` is specified, a port gets its
+    segmentation type from the network its connected to.
+  in: body
+  required: true
+  type: string
+segmentation_type-request:
+  description: |
+    The segmentation type for the subport. Possible values include ``vlan``
+    and ``inherit``. When ``inherit`` is specified, a port gets its
+    segmentation type from the network its connected to.
   in: body
   required: false
   type: string

api-ref/source/v2/trunk.inc

@@ -157,7 +157,7 @@ Request
 
    - trunk_id: trunk_id
    - segmentation_id: segmentation_id
-   - segmentation_type: segmentation_type
+   - segmentation_type: segmentation_type-request
    - port_id: port_id_subport
 
 Request Example