Fix crash in AllInOneTetherSettings when user is not admin

When user is not admin, we should skip the setup and tear down
procedures in AllInOneTetherSettings' lifecycle. Also, the switch for
"Hotspot & tethering" on "Network & internet" should be disabled in such
case.

Bug: 151648198
Test: Build and flashed to crosshatch device. Using guest user, the
settings won't crash when using AllInOneTetherSetting and the switch is
disabled.

Change-Id: Ibd2f4111c53b8b9fa6a18504a681a27b966a3c46