msix: fix msix_vector_masked

commit 428c3ece97 ("fix MSI injection on Xen")
inadvertently enabled the xen-specific logic unconditionally.
Limit it to only when xen is enabled.
Additionally, msix data should be read with pci_get_log
since the format is pci little-endian.

Reported-by: "Daniel P. Berrange" <berrange@redhat.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/pci/msix.c

@@ -80,10 +80,10 @@ static void msix_clr_pending(PCIDevice *dev, int vector)
 static bool msix_vector_masked(PCIDevice *dev, unsigned int vector, bool fmask)
 {
     unsigned offset = vector * PCI_MSIX_ENTRY_SIZE;
-    uint32_t *data = (uint32_t *)&dev->msix_table[offset + PCI_MSIX_ENTRY_DATA];
+    uint8_t *data = &dev->msix_table[offset + PCI_MSIX_ENTRY_DATA];
     /* MSIs on Xen can be remapped into pirqs. In those cases, masking
      * and unmasking go through the PV evtchn path. */
-    if (xen_is_pirq_msi(*data)) {
+    if (xen_enabled() && xen_is_pirq_msi(pci_get_long(data))) {
         return false;
     }
     return fmask || dev->msix_table[offset + PCI_MSIX_ENTRY_VECTOR_CTRL] &