network: dhcp-pd: add 6rd support

Closes #19152.

network/80-6rd-tunnel.network

@@ -0,0 +1,18 @@
+#  SPDX-License-Identifier: LGPL-2.1-or-later
+#
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+
+# This network file matches 6rd-* SIT devices which is automatically created by
+# systemd-networkd when DHCPv4 6RD option is received.
+
+[Match]
+Name=6rd-*
+Type=sit
+
+[Network]
+DHCPPrefixDelegation=yes

network/meson.build

@@ -1,7 +1,8 @@
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
 if conf.get('ENABLE_NETWORKD') == 1
-        install_data('80-container-host0.network',
+        install_data('80-6rd-tunnel.network',
+                     '80-container-host0.network',
                      '80-container-ve.network',
                      '80-container-vz.network',
                      '80-vm-vt.network',