Fix ConnectivityManagerTest#testFactoryReset flaky

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
1 file changed