Fix compiling on OpenBSD

1. The `net/if_types.h` header does not define the `IFT_STF` symbol.
2. The `netinet6/in6_var.h` header defines some of the used symbols.

For the reference, see:
 - https://codeberg.org/OpenBSD/ports/src/commit/f8f1aedbe8aff550c69930b5d92b9c392e298382/x11/qt6/qtbase/patches/patch-src_network_kernel_qnetworkinterface_unix_cpp


--- a/qtbase/src/network/kernel/qnetworkinterface_unix.cpp
+++ b/qtbase/src/network/kernel/qnetworkinterface_unix.cpp
@@ -392,6 +392,9 @@ QT_BEGIN_INCLUDE_NAMESPACE
 #  include <net/if_media.h>
 #  include <net/if_types.h>
 #  include <netinet/in_var.h>
+#  ifdef Q_OS_OPENBSD
+#    include <netinet6/in6_var.h>
+#  endif
 #endif // QT_PLATFORM_UIKIT
 QT_END_INCLUDE_NAMESPACE
 
@@ -419,7 +422,9 @@ static QNetworkInterface::InterfaceType probeIfType(int socket, int iftype, stru
         return QNetworkInterface::Ieee1394;
 
     case IFT_GIF:
+#ifndef Q_OS_OPENBSD
     case IFT_STF:
+#endif
         return QNetworkInterface::Virtual;
     }