Scan Optimization: expose API to update device mobility state

Exposed API in WifiManager to allow device mobility state to
be updated, so that Wifi scan interval can be increased when the
device is stationary in order to save power. Also added a new
permission to protect this API from being used by unauthorized
applications.

Bug: 120097108
Test: Call new API method using test app
Change-Id: Iee59dba711c23add5d4b2affafeac2c009407c7f