Fix compilation on Windows without precompiled headers

qnetworkinterface_win_p.h needs to include at least one Qt header before
it can use QT_BEGIN_NAMESPACE. That header is the first header in
qnetworkinterface_win.cpp.

Found when trying to compile Qt with ICC.

Change-Id: Iaa312ff54243b6fb3beb107f0eda74f92c6e3ebb
Reviewed-by: Richard J. Moore <rich@kde.org>

src/network/kernel/qnetworkinterface_win_p.h

@@ -53,6 +53,7 @@
 // We mean it.
 //
 
+#include <QtCore/qglobal.h>
 #include <winsock2.h>
 #include <qt_windows.h>
 #include <time.h>