enable rtadvd in usr.sbin/Makefile.

rcsid police on usr.sbin/rtadvd.
add sample config into etc/rtadvd.conf.
add files into distrib/sets/list.

src/etc/rtadvd.conf

@@ -0,0 +1,19 @@
+#	$OpenBSD: rtadvd.conf,v 1.1 1999/12/11 10:33:26 itojun Exp $
+#	$NetBSD: rtadvd.conf,v 1.3 1999/07/03 20:50:39 hubertf Exp $
+#
+# common definitions.
+#
+default:\
+	:chlim#64:raflags#0:rltime#1800:rtime#30000:retrans#1000:\
+	:pinfoflags#192:vltime#3600000:pltime#3600000:mtu#1500:
+ether:\
+	:mtu#1500:tc=default:
+#
+# interfaces.
+#
+# This is a sample entry.  You'll need to have an entry like this
+# for each of your interfaces on which you'll be advertising about the prefix
+# information.
+# Then, list name of the interfaces to be advertised onto the command line.
+#ef0:\
+#	:addrs#1:addr="fec0:0000:0000:0000::":prefixlen#64:tc=ether: