mxrouterctl: Do not enable IPv6 routing

We don't use ipv6 currently. There might be problems if ipv6 routing is
enabled, e.g. potential reachability without the appropriate filewall
rules.

For now, just don't enable it.

mxrouter/mxrouterctl

@@ -525,10 +525,10 @@ sub start {
 			unless exists $want_route->{$_};
 	}
 
-	unless (get_ipv6_forwarding()>0) {
-		warn "enable IPV6 forwarding\n" unless $opt_quiet;
-		set_ipv6_forwarding(1);
-	}
+#	unless (get_ipv6_forwarding()>0) {
+#		warn "enable IPV6 forwarding\n" unless $opt_quiet;
+#		set_ipv6_forwarding(1);
+#	}
 
 	unless (get_ipv4_routing()>0) {
 		warn "enable IPV4 routing\n" unless $opt_quiet;