Switch to WifiManager.{start,stop}SoftAp()

Test: as follows
    - built
    - flashed
    - booted
    - "runtest frameworks-net" passes
Bug: 31466854

Change-Id: I730d029128a14b936c111ae159b9708d935f4656
(cherry picked from commit ceb54c63dc7af8f11ec9eac4993a43b9e788ee2f)
2 files changed