This marks FreeBSD GCE images as gVNIC capable by adding the
--guest-os-features=GVNIC flag at creation time as suggested in GCE
documentation[1]. This allows Generation 3 and newer GCE instances
to leverage advanced networking capabilities and performance
enhancements provided by gVNIC. Users will benefit from these
improvements without needing to create custom images.
[1] https://cloud.google.com/compute/docs/networking/using-gvnic#create_a_vm_with_gvnic_support
MFC after: 3 days