networkd: add basic Varlink interface

Let's get networkd onto Varlink. This only adds the most basic of
operations.

I'd love to see networkd do Varlink for all its basic operations so that
networkctl can use that, and work correctly before D-Bus is up. Right
now, many of networkctls calls simply don't work before D-Bus, and I'd
like to see that improved.

src/shared/meson.build

@@ -176,9 +176,10 @@ shared_sources = files(
         'varlink-io.systemd.Credentials.c',
         'varlink-io.systemd.Journal.c',
         'varlink-io.systemd.ManagedOOM.c',
+        'varlink-io.systemd.Network.c',
         'varlink-io.systemd.PCRExtend.c',
-        'varlink-io.systemd.Resolve.Monitor.c',
         'varlink-io.systemd.Resolve.c',
+        'varlink-io.systemd.Resolve.Monitor.c',
         'varlink-io.systemd.UserDatabase.c',
         'varlink-io.systemd.oom.c',
         'varlink-io.systemd.service.c',

src/shared/varlink-io.systemd.Network.c

@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "varlink-io.systemd.Network.h"
+
+static VARLINK_DEFINE_METHOD(GetStates,
+                             VARLINK_DEFINE_OUTPUT(AddressState, VARLINK_STRING, 0),
+                             VARLINK_DEFINE_OUTPUT(IPv4AddressState, VARLINK_STRING, 0),
+                             VARLINK_DEFINE_OUTPUT(IPv6AddressState, VARLINK_STRING, 0),
+                             VARLINK_DEFINE_OUTPUT(CarrierState, VARLINK_STRING, 0),
+                             VARLINK_DEFINE_OUTPUT(OnlineState, VARLINK_STRING, 0),
+                             VARLINK_DEFINE_OUTPUT(OperationalState, VARLINK_STRING, 0));
+
+static VARLINK_DEFINE_METHOD(GetNamespaceId,
+                             VARLINK_DEFINE_OUTPUT(NamespaceId, VARLINK_INT, 0));
+
+VARLINK_DEFINE_INTERFACE(
+                io_systemd_Network,
+                "io.systemd.Network",
+                &vl_method_GetStates,
+                &vl_method_GetNamespaceId);

src/shared/varlink-io.systemd.Network.h

@@ -0,0 +1,6 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include "varlink-idl.h"
+
+extern const VarlinkInterface vl_interface_io_systemd_Network;