WifiManager: allow setWifiApConfiguration to return false

The api for setWifiApConfiguration allows for config saves to return
false, but the implementation always returns true (if there wasn't an
exception thrown).  This CL allows the API to actually return false and
adds unittests.

Bug: 67601382
Test: frameworks/base/wifi/tests/runtests.sh
Test: frameworks/opt/net/wifi/tests/wifitests/runtests.sh
Test: manually update ap config in settings and verify save
Test: wifi integration tests
Change-Id: I038ab68f5fc4bf22df5b61d329077eacda547338