Fix bond_mode enum 802.1ad -> 802.3ad

This seems to me a clerical error made a long time ago in the spec [1].
The 802.1ad values does not seems to be a valid bonding mode but 802.3ad
does.

This patch fixes the schema in the nova doc. No test are changed as nova
does not generate this part of the network metadata.

[1] https://specs.openstack.org/openstack/nova-specs/specs/kilo/approved/metadata-service-network-info.html#rest-api-impact

Change-Id: I0055d13b055e34372a8186008ba75be68aa2edf9
Closes-Bug: #1925388

doc/api_schemas/network_data.json

@@ -175,7 +175,7 @@
           "type": "string",
           "title": "Port bonding type",
           "enum": [
-            "802.1ad",
+            "802.3ad",
             "balance-rr",
             "active-backup",
             "balance-xor",
@@ -184,7 +184,7 @@
             "balance-alb"
           ],
           "examples": [
-            "802.1ad"
+            "802.3ad"
           ]
         },
         "bond_links": {