WifiManager: implement start/stopLocalOnlyHotspot

Implement new calls to startLocalOnlyHotspot and
cancelLocalOnlyHotspotRequest along with the classes
LocalOnlyHotspotCallback and LocalOnlyHotspotReservation.

Added tests for starting LOHS and cancelling a LOHS request.

The calls will be exposed in a later CL.

Bug: 36704763
Test: compiles
Test: frameworks/base/wifi/tests/runtests.sh
Test: frameworks/opt/net/wifi/tests/wifitests/runtests.sh

Change-Id: If54a89cb8dfd235bc18ef3e6c89f9d30882136a3