P2P: Set wifi preferred channels when the supplicant is started.

Set wifi preferred channels when the supplicant is started, if
there are any safe channels from the previous LTE event received
from RIL. This is to ensure that p2p GO is always started on one
safe channels.

Change-Id: Ib0c36dbc4dfdec3721adb2f72d604158eeff9a87
CRs-Fixed: 523207