networkctl,networkd: add --no-reconfigure flag to networkctl reload

Add a new --no-reconfigure flag to 'networkctl reload' that reloads
.network and .netdev files from disk without reconfiguring any network
interfaces. This may be useful to avoid reconfiguring multiple interfaces
simultaneously when multiple .network files are updated, or when an updated
.network file is applied to multiple interfaces.

On the networkd side, manager_reload() gains a reconfigure_links parameter
that gates the per-link reconfiguration loop. A new io.systemd.Network.Reload
varlink method is added that exposes this as an optional reconfigureLinks
boolean (defaults to true). Both plain 'networkctl reload' and
'--no-reconfigure' now unconditionally call this method first. If an older
networkd returns MethodNotFound, plain reload falls back to
io.systemd.service.Reload for backward compatibility; '--no-reconfigure'
fails with a clear error in that case.

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

@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
+#include "bus-polkit.h"
 #include "varlink-io.systemd.Network.h"
 
 /* Helper macro to define address fields with both binary and string representation */
@@ -544,6 +545,12 @@ SD_VARLINK_DEFINE_STRUCT_TYPE(
                 SD_VARLINK_FIELD_COMMENT("Current transmit/receive bitrates from speed meter"),
                 SD_VARLINK_DEFINE_FIELD_BY_TYPE(BitRates, BitRates, SD_VARLINK_NULLABLE));
 
+static SD_VARLINK_DEFINE_METHOD(
+                Reload,
+                SD_VARLINK_FIELD_COMMENT("If true (default), reload config files and reconfigure all matching network interfaces. If false, only reload config files without reconfiguring interfaces; use 'networkctl reconfigure' afterwards to apply changes selectively."),
+                SD_VARLINK_DEFINE_INPUT(reconfigureLinks, SD_VARLINK_BOOL, SD_VARLINK_NULLABLE),
+                VARLINK_DEFINE_POLKIT_INPUT);
+
 static SD_VARLINK_DEFINE_METHOD(
                 Describe,
                 SD_VARLINK_FIELD_COMMENT("All network interfaces managed by systemd-networkd"),
@@ -612,6 +619,7 @@ SD_VARLINK_DEFINE_INTERFACE(
                 &vl_method_GetStates,
                 &vl_method_GetNamespaceId,
                 &vl_method_GetLLDPNeighbors,
+                &vl_method_Reload,
                 &vl_method_SetPersistentStorage,
                 &vl_type_Address,
                 &vl_type_BitRates,