Use complete types in container declarations

Qt 6 disallows to use incomplete types in container declarations
in some cases, e.g. in parameters of signals/slots.

src/base/net/reverseresolution.h

@@ -29,9 +29,9 @@
 #pragma once
 
 #include <QCache>
+#include <QHostAddress>
 #include <QObject>
 
-class QHostAddress;
 class QHostInfo;
 class QString;