IP Restriction on Azure WebApp from ARM (Azure Resource Manager)

That setting is for allowed IP address rather than exclusions - you can set via https://resources.azure.com/

Usage example is:

"ipSecurityRestrictions": [
  {
    "ipAddress": "12.23.254.3",
    "subnetMask": "255.255.0.0"
  }
]

I've had to add siteConfig and place the ipSecurityRestrictions there to make it work:

{
    "apiVersion": "2015-06-01",
    "name": "[parameters('siteName')]",
    "type": "Microsoft.Web/Sites",
    ...
    "properties":{
        "siteConfig":{
            "ipSecurityRestrictions" : {
                 "ipAddress": "123.123.123.123"
            }
        }
    },
    "resources" : {
        ...
    }
}