busybox: 
 * use "ifconfig" for multid, now working because of FREETZ_BUSYBOX_FEATURE_IFUPDOWN_IPV6
 * no need for FREETZ_BUSYBOX_IP (which was not selected)
(refs #1786)

git-svn-id: file:///var/svn/freetz/trunk@9950 149334a1-2f27-0410-a3b9-fc62619ac1e6