Put the _unbound user in "unbound" login class; unbound uses setusercontext

to initialize the unprivileged user, so the usual rc.d mechanism to set the
class isn't used. Problem reported by otto, ok otto@ ajacoutout@

src/etc/master.passwd

@@ -9,7 +9,7 @@ _rstatd:*:30:30::0:0:rpc.rstatd:/var/empty:/sbin/nologin
 _rusersd:*:32:32::0:0:rpc.rusersd:/var/empty:/sbin/nologin
 _fingerd:*:33:33::0:0:fingerd:/var/empty:/sbin/nologin
 _x11:*:35:35::0:0:X Server:/var/empty:/sbin/nologin
-_unbound:*:53:53::0:0:Unbound Daemon:/var/unbound:/sbin/nologin
+_unbound:*:53:53:unbound:0:0:Unbound Daemon:/var/unbound:/sbin/nologin
 _spamd:*:62:62::0:0:Spam Daemon:/var/empty:/sbin/nologin
 uucp:*:66:1::0:0:UNIX-to-UNIX Copy:/var/spool/uucppublic:/sbin/nologin
 www:*:67:67::0:0:HTTP Server:/var/www:/sbin/nologin