networkd: change SendRelease default to true

Now that we don't drop DHCP config on restart, this seems appropriate.

man/systemd.network.xml

@@ -1568,7 +1568,7 @@
           <term><varname>SendRelease=</varname></term>
           <listitem>
             <para>When true, the DHCPv4 client sends a DHCP release packet when it stops.
-            Defaults to false.</para>
+            Defaults to true.</para>
           </listitem>
         </varlistentry>
 

src/network/networkd-network.c

@@ -371,6 +371,7 @@ int network_load_one(Manager *manager, const char *filename) {
                 .dhcp_use_routes = true,
                 /* NOTE: this var might be overwritten by network_apply_anonymize_if_set */
                 .dhcp_send_hostname = true,
+                .dhcp_send_release = true,
                 /* To enable/disable RFC7844 Anonymity Profiles */
                 .dhcp_anonymize = false,
                 .dhcp_route_metric = DHCP_ROUTE_METRIC,