msix: Add SystemAllocator to MsixConfig

The point here is to let MsixConfig take care of the GSI allocation,
which means the SystemAllocator must be passed from the vmm crate all
the way down to the pci crate.

Once this is done, the GSI allocation and irq_fd creation is performed
by MsixConfig directly.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vm-virtio/src/transport/pci_device.rs

@@ -256,6 +256,7 @@ impl VirtioPciDevice {
         device: Arc<Mutex<dyn VirtioDevice>>,
         msix_num: u16,
         iommu_mapping_cb: Option<Arc<VirtioIommuRemapping>>,
+        allocator: &mut SystemAllocator,
     ) -> Result<Self> {
         let device_clone = device.clone();
         let locked_device = device_clone.lock().unwrap();
@@ -276,7 +277,7 @@ impl VirtioPciDevice {
         let pci_device_id = VIRTIO_PCI_DEVICE_ID_BASE + locked_device.device_type() as u16;
 
         let (msix_config, msix_config_clone) = if msix_num > 0 {
-            let msix_config = Arc::new(Mutex::new(MsixConfig::new(msix_num)));
+            let msix_config = Arc::new(Mutex::new(MsixConfig::new(msix_num, allocator)));
             let msix_config_clone = msix_config.clone();
             (Some(msix_config), Some(msix_config_clone))
         } else {