radvd: add /etc/radvd.conf

When starting radvd without any configuration the following errors would
be triggered.

"""
root@intel-x86-64:~# systemctl status radvd
● radvd.service - Router advertisement daemon for IPv6
Loaded: loaded (/lib/systemd/system/radvd.service; enabled; vendor preset:
	enabled)
Active: inactive (dead)
        Condition: start condition failed at Tue 2019-09-24 13:29:36 UTC; 3s ago
	    └─ ConditionPathExists=/etc/radvd.conf was not met
"""

Normally the user should create and configrue the /etc/radvd.conf
manually.  However the radvd provide a example file for redhad located
at "radvd/redhat/radvd.conf.empty". When installing, it would copy
radvd/redhat/radvd.conf.empty to /etc/radvd.conf. Also add this empty
conf here to used as an example of configuration

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-networking/recipes-daemons/radvd/files/radvd.conf

@@ -0,0 +1,18 @@
+# NOTE: there is no such thing as a working "by-default" configuration file. 
+#       At least the prefix needs to be specified.  Please consult the radvd.conf(5)
+#       man page and/or /usr/share/doc/radvd-*/radvd.conf.example for help.
+#
+#
+#interface eth0
+#{
+#	AdvSendAdvert on;
+#	MinRtrAdvInterval 30;
+#	MaxRtrAdvInterval 100;
+#	prefix 2001:db8:1:0::/64
+#	{
+#		AdvOnLink on;
+#		AdvAutonomous on;
+#		AdvRouterAddr off;
+#	};
+#
+#};

meta-networking/recipes-daemons/radvd/radvd.inc

@@ -18,7 +18,8 @@ SRC_URI = "http://v6web.litech.org/radvd/dist/radvd-${PV}.tar.gz \
            file://radvd.init \
            file://radvd.service \
            file://volatiles.03_radvd \
-           file://radvd.default"
+           file://radvd.default \
+           file://radvd.conf"
 
 inherit autotools useradd pkgconfig systemd
 
@@ -52,6 +53,8 @@ do_install_append () {
     for i in radvd.conf.example README; do \
         install -m 0644 ${S}/$i ${D}${docdir}/radvd; \
     done
+
+    install -m 0644 ${WORKDIR}/radvd.conf ${D}${sysconfdir}/radvd.conf
 }
 
 USERADD_PACKAGES = "${PN}"