nwfilter: Add missing driver lock in qemu driver

This adds a missing driver lock in the qemu driver to protect
the list of domains.

src/qemu/qemu_driver.c

@@ -11874,11 +11874,15 @@ static virStateDriver qemuStateDriver = {
 };
 
 static int
-qemudVMFilterRebuild(virConnectPtr conn,
+qemudVMFilterRebuild(virConnectPtr conn ATTRIBUTE_UNUSED,
                      virHashIterator iter, void *data)
 {
-    (void)conn;
+    struct qemud_driver *driver = qemu_driver;
+
+    qemuDriverLock(driver);
     virHashForEach(qemu_driver->domains.objs, iter, data);
+    qemuDriverUnlock(driver);
+
     return 0;
 }