Add NETWORK_FACTORY permission

The permission check in
ConnectivityService#registerNetworkFactory has been changed to
NETWORK_FACTORY. Add this permission to bluetooth
app because bluetooth tethering requires call this API.

Bug: 32963470
Test: - atest PanServiceTest
      - Test BT PAN service manually

Change-Id: I0b123e77420d339219c079df9928946ca1f3b2a9