pci_emul_add_msixcap
int pci_emul_add_msixcap(struct pci_devinst *pi, int msgnum, int barnum);
error = pci_emul_add_msixcap(pi, sc->max_queues + 1, NVME_MSIX_BAR);
if (pci_emul_add_msixcap(vs->vs_pi, nvec, VIRTIO_MSIX_BAR) != 0)