want PHD tests exercising VNICs #1050

It's unfortunate that issues which impacted viona NICs, such as #1045, #1048, and so on, were not caught by CI when they were introduced, and instead only were discovered by manual testing much later in the game. We should really figure out a way to exercise VNICs in our test suite.

This might be a bit of a lift, as it would take a bit of work inside the guest to get it to actually do its half of using the NIC and actually checking if it works. Probably will require some additional stuff in the guest OS adapters to run the correct commands for different guest OSes. But it seems worth having.