Fix v3 api-ref for updating extra specs of volume type

In v3 api-ref for updating extra specs of volume type, the request and
response contents are wrongly described, and also the HTTP method and
URL are not correct. This patch addes new api-ref for it.

Change-Id: I4263c25a0638a68d0d102c7966ebb77604c019fc

api-ref/source/v3/samples/volume-type-extra-specs-create-update-request.json

@@ -0,0 +1,6 @@
+{
+    "extra_specs": {
+        "key1": "value1",
+        "key2": "value2"
+    }
+}

api-ref/source/v3/samples/volume-type-extra-specs-create-update-response.json

@@ -0,0 +1,6 @@
+{
+    "extra_specs": {
+        "key1": "value1",
+        "key2": "value2"
+    }
+}

api-ref/source/v3/volumes-v3-types.inc

@@ -67,12 +67,13 @@ Response Example
    :language: javascript
 
 
-Update extra specs for volume type
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Create or update extra specs for volume type
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-.. rest_method::  PUT /v3/{project_id}/types/{volume_type_id}
+.. rest_method::  POST /v3/{project_id}/types/{volume_type_id}/extra_specs
 
-Updates the extra specifications that are assigned to a volume type.
+Adds new extra specifications to a volume type, or updates the extra
+specifications that are assigned to a volume type.
 
 
 Normal response codes: 200
@@ -85,13 +86,12 @@ Request
 
    - project_id: project_id_path
    - volume_type_id: volume_type_id
-   - volume_type: volume_type_1
    - extra_specs: extra_specs
 
 Request Example
 ---------------
 
-.. literalinclude:: ./samples/volume-type-update-request.json
+.. literalinclude:: ./samples/volume-type-extra-specs-create-update-request.json
    :language: javascript
 
 
@@ -101,17 +101,13 @@ Response Parameters
 
 .. rest_parameters:: parameters.yaml
 
-   - volume_type: volume_type_1
-   - is_public: is_public
    - extra_specs: extra_specs
-   - description: description_15
-   - name: name_7
 
 
 Response Example
 ----------------
 
-.. literalinclude:: ./samples/volume-type-show-response.json
+.. literalinclude:: ./samples/volume-type-extra-specs-create-update-response.json
    :language: javascript