Add Missing Scenario for IP Address Change

IP Address of service changes when customer switches subnet of service. This is because we create a new deployment. Need to explicitly doc this since a customer ran into this issue.

Author: tehnoonr

articles/api-management/api-management-howto-ip-addresses.md

@@ -128,6 +128,7 @@ In the Developer, Basic, Standard, and Premium tiers of API Management, the publ
 * The service subscription is [suspended](https://github.com/Azure/azure-resource-manager-rpc/blob/master/v1.0/subscription-lifecycle-api-reference.md#subscription-states) or [warned](https://github.com/Azure/azure-resource-manager-rpc/blob/master/v1.0/subscription-lifecycle-api-reference.md#subscription-states) (for example, for nonpayment) and then reinstated.
 * (Developer and Premium tiers) Azure Virtual Network is added to or removed from the service.
 * (Developer and Premium tiers) API Management service is switched between external and internal VNet deployment mode.
+* (Developer and Premium tiers) API Management service is moved to a different subnet
 * (Premium tier) [Availability zones](../reliability/migrate-api-mgt.md) are enabled, added, or removed.
 * (Premium tier) In [multi-regional deployments](api-management-howto-deploy-multi-region.md), the regional IP address changes if a region is vacated and then reinstated.