This issue is fixed in Oracle Hardware Management Pack 2.3.2.2 (see note below).
The fwupdate nic-controller-firmware command that was added in Oracle Hardware Management Pack 2.3.1 cannot currently be used to update the Sun Server X4-8 onboard Ethernet controller.
However, the Ethernet controllers on installed PCIe network interface cards (NICs) can be updated with this command.
Workaround
Use a different method, such as Oracle System Assistant, to update the Sun Server X4-8 onboard Ethernet controller.
If you are using Oracle Hardware Management Pack 2.3.3 or later, you can also use fwupdate on systems with supported Linux or Microsoft Windows operating systems to update Ethernet controllers.