wifi-service: Add a class for scan available settings compatibility

Settings.Global.WIFI_SCAN_ALWAYS_AVAILABLE which is marked @hide is used
extensively by external apps. Even though the wifi stack stopped using
the setting, we need to provide compatibility support for set/get of
that setting.

Bug: 149954910
Test: Device boots up and connects to wifi networks.
Test: Manually verification:
Getter:
 - Change the scan available state from settings app (uses WifiManager.
 setScanAlwaysAvailable())
 -'adb shell settings get global wifi_scan_always_enabled'

Setter:
 -'adb shell settings put global wifi_scan_always_enabled 1'
 - Verified scan available state from settings app (uses WifiManager.
 isScanAlwaysAvailable).

(cherry-picked from ag/10384217)

Test: atest com.android.server.wifi
Change-Id: I64b5d4d16eab1cda6c186153958601f41f7bcae7
7 files changed
tree: 948e58aedb4d5aa57f2291133aa8b300f66731b2
  1. apex/
  2. service/
  3. PREUPLOAD.cfg