WifiManager: Expose enableWifiConnectivityManager

Rename enableWifiConnectivityManager to allowAutoJoin and expose it as a
@SystemApi for OEM's to dynamically toggle on/off auto join status.

Bug: 141889280
Test: Compiles
Change-Id: I0dc5141cd2f751ddf199ce9b2b2ecce564f1b475
4 files changed