The Hardware Devices Tab was removed from the Service Definitions tab in the UI for NSX-V in the vSphere Client.
VMware NSX for vSphere 6.4.x
The Hardware Devices tab is not supported post NSX-V 6.4.7, as noted in the following link:
https://docs.vmware.com/en/VMware-NSX-Data-Center-for-vSphere/6.4/rn/nsx-vsphere-client-65-functionality-support.html