Notify scan-only mode to driver for power saving

If Wi-Fi driver knows it's in scan-only mode, it can save more power
than connect mode.

This change adds setScanMode in IWifiStaIface to allow Wi-Fi framework
to notify scan-only mode change to Wi-Fi driver.

Bug: 177811719
Test: atest com.android.server.wifi

Change-Id: Ifa8a3d0c8dc105bbf9e42b7b17b1061b38714199
5 files changed