Do not start radvd when dhcp6c is stopping

Every time the state is changed in dhcp6c, it will call /sbin/dhcp6c-state, which is symlinked to rc. dhcp6c_state_main will be executed and radvd is started (httpd is also restarted for some reason).

If stop_dhcp6c is called and dhcp6c is running, radvd will always be started and happily starts advertising, leading to time outs / long connection times to some websites that are available over both IPv4 and IPv6 (like Google).

For some reason switching the stop_dhcp6c and stop_radvd statements at several places didn't work as I expected it to: radvd would still be running (restarted).
Perhaps this was caused by the rapid stop_radv/start_radvd/stop_radvd call in combination with radvd spawning two processes while daemonizing itself.