Need to append new instances to VNIC's secondary-macs link property #1372
Description
Part of the external IP workaround involves convincing the world that the underlay VNIC net0 has the guest MAC address (in addition to its own). This is so traffic destined for the guest can actually get to OPTE through the VNIC, which would normally ignore most L2 packets with a MAC different from its own. We do that by setting the secondary-macs link property on the VNIC, here. That needs to append, not overwrite, the new guest MAC to the list of secondary MACs for the VNIC. Otherwise we can only have one guest at a time on the host.
We'll need to keep the list of applied secondary MACs around (for all non-deleted OPTE ports), and we'll probably want to remove the MAC when the instance is stopped.