package/radvd: disable by default in systemd preset-all

We don't provide a configuration file, so disable radvd by default.

Update the help message with instructions on how to enable radvd at
build time with systemd.

Signed-off-by: Carlos Santos <unixmania@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/radvd/50-radvd.preset

@@ -0,0 +1 @@
+disable radvd.service

package/radvd/Config.in

@@ -5,4 +5,12 @@ config BR2_PACKAGE_RADVD
 	help
 	  IPv6 Router Advertisement Daemon.
 
+	  On busybox and sysvinit systems, radvd will be started only if
+	  a /etc/radvd.conf exists.
+
+	  To enable it at build time with systemd, add /etc/radvd.conf
+	  and a /etc/systemd/system-preset/40-radvd.preset file with
+
+	    enable radvd.service
+
 	  http://www.litech.org/radvd/

package/radvd/radvd.mk

@@ -17,6 +17,12 @@ RADVD_AUTORECONF = YES
 RADVD_LICENSE = BSD-4-Clause-like
 RADVD_LICENSE_FILES = COPYRIGHT
 
+# We don't provide /etc/radvd.conf, so disable the service by default.
+define RADVD_INSTALL_INIT_SYSTEMD
+	$(INSTALL) -D -m 0644 package/radvd/50-radvd.preset \
+		$(TARGET_DIR)/usr/lib/systemd/system-preset/50-radvd.preset
+endef
+
 define RADVD_INSTALL_INIT_SYSV
 	$(INSTALL) -D -m 0755 package/radvd/S50radvd $(TARGET_DIR)/etc/init.d/S50radvd
 endef