message: Expose new Enum values for VirtualNetworkGateway sizes.
  Add new enum values to VirtualNetworkGateway tier and name enums.
diff: "properties": {
  "name": {
  "type": "string",
  - "description": "Gateway SKU name. Possible values are: 'Basic', 'HighPerformance','Standard', and 'UltraPerformance'.",
  + "description": "Gateway SKU name. Possible values are: 'Basic', 'HighPerformance','Standard', 'UltraPerformance', 'VpnGw1', 'VpnGw2' and 'VpnGw3'.",
  "enum": [
  "Basic",
  "HighPerformance",
  "Standard",
  - "UltraPerformance"
  + "UltraPerformance",
  + "VpnGw1",
  + "VpnGw2",
  + "VpnGw3"
  ],
  "x-ms-enum": {
  "name": "VirtualNetworkGatewaySkuName",
  },
  "tier": {
  "type": "string",
  - "description": "Gateway SKU tier. Possible values are: 'Basic', 'HighPerformance','Standard', and 'UltraPerformance'.",
  + "description": "Gateway SKU tier. Possible values are: 'Basic', 'HighPerformance','Standard', 'UltraPerformance', 'VpnGw1', 'VpnGw2' and 'VpnGw3'.",
  "enum": [
  "Basic",
  "HighPerformance",
  "Standard",
  - "UltraPerformance"
  + "UltraPerformance",
  + "VpnGw1",
  + "VpnGw2",
  + "VpnGw3"
  ],
  "x-ms-enum": {
  "name": "VirtualNetworkGatewaySkuTier",
  