Currently legacy VPN only works on IPv4, and it should always
turn down when the addresses are changed. It assumed that the
interface will be brought down and up, so the event can be
detected via interfaceStatusChanged(). However, the assumption
was incorrect and the event is actually driver-dependent. To
fix this issue, ConnectivityService now tells VPN that the
interface is down when resetting IPv4 addresses.
Change-Id: I76d15e56552d86635c5b274ca980be5da905a6fb
0c074e6843