30b450774e
When we roam between networks and our link-state goes down, automatically remove the IPv6-Only flag from the interface. Otherwise we might switch from an IPv6-only to and IPv4-only network and the flag would stay and we would prevent IPv4 from working. While the actual function call to clear the flag is under EXPERIMENTAL, the eventhandler is not as we might want to re-use it for other functionality on link-down event (such was re-calculate default routers for example if there is more than one). Reviewed by: hrs Differential Revision: https://reviews.freebsd.org/D19487