hostdev: Only rollback detach of managed devices on error

Since we don't detach unmanaged devices before attaching them to a
domain, we shouldn't reattach them to rollback an error either.

src/util/virhostdev.c

@@ -711,6 +711,7 @@ virHostdevPreparePCIDevices(virHostdevManagerPtr hostdev_mgr,
     for (i = 0; i < virPCIDeviceListCount(pcidevs); i++) {
         virPCIDevicePtr dev = virPCIDeviceListGet(pcidevs, i);
 
+        if (virPCIDeviceGetManaged(dev)) {
             /* NB: This doesn't actually re-bind to original driver, just
              * unbinds from the stub driver
              */
@@ -718,6 +719,7 @@ virHostdevPreparePCIDevices(virHostdevManagerPtr hostdev_mgr,
                                               hostdev_mgr->activePCIHostdevs,
                                               hostdev_mgr->inactivePCIHostdevs));
         }
+    }
 
  cleanup:
     virObjectUnlock(hostdev_mgr->activePCIHostdevs);