For clarrity, to test MSI even though error PCI_ERR_ENOTSUP is reported, I have commented out our check for PVM support.
 As said, from a send/receive perspective, in QEmu VM, it seems to be working. I just need validation this is a valid 
way forwards, or do we need an alternative mask/unmask besides the MSI API?

if (capid == CAPID_MSI) {                                                    
    cap_msi_mask_t mask;                                                     
                                                                             
    r = cap_msi_get_irq_mask(dev->hdl, dev->msi_cap, &mask);                 
                                                                             
    if (r == PCI_ERR_ENOTSUP) {                                              
        log_err("capability 0x%02x (MSI) Per Vector Masking (PVM) not "      
                "supported\n", capid);                                       
                                                                             
        //msix_uninit(dev);                                                  
        //return r;                                                          
    }                                                                        
    else if (r != PCI_ERR_OK) {                                              
        log_err("cap_msi_get_irq_mask error; %s\n", pci_strerror(r));        
                                                                             
        msix_uninit(dev);                                                    
        return r;                                                            
    }                                                                        
}