Better synchronize RA & DHCPv6 events
Accumulate some events to avoid flooding
Restart softwires for address and prefix changes

Signed-off-by: Steven Barth <steven@midlink.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46518 3c298f89-4303-0410-b956-a3cf2f4a3e73