Allow wificond to set interfaces up and down

This is apparently a privileged ioctl.  Being able to do this allows us
to no longer kill hostapd with SIGTERM, since we can cleanup after hard
stops.

Bug: 31023120
Test: wificond unit and integration tests pass

Change-Id: Icdf2469d403f420c742871f54b9fb17432805991
(cherry picked from commit ca7b04ba)