This change fixed two things:
1. start wifi tethering after airplane mode enabled.
2. run ConnectivityManager#factoryReset with TETHER_PRIVILEGED
permission, so it can sucessfully stop tethering.
Orignally testFactoryReset don't actually test stop tethering.
Tethering already be stopped while airplane mode enabled, but
enable airplane mode then doing factory reset would have race in
wifi stack which caused airplane mode don't take effect in wifi
side.
Bug: 240677322
Test: atest ConnectivityManagerTest#testFactoryReset --iterations 50
Change-Id: I3185401b10b798af744df5c3c7c21fee3d418939
b7ed4a2784