In doc "Installing a cluster on Azure into an existing VNet"[1], only list few ports required to to be accessed in network security group, but actually, additional ports described in azure upi doc[2] are also required here.
Suggest to add those ports to doc [1] as well to avoid installation failure.

[1] https://docs.openshift.com/container-platform/4.15/installing/installing_azure/installing-azure-vnet.html#installation-about-custom-azure-vnet-nsg-requirements_installing-azure-vnet
[2] https://docs.openshift.com/container-platform/4.15/installing/installing_azure/installing-azure-user-infra.html#installation-network-connectivity-user-infra_installing-azure-user-infra                    

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