Assume tethering is enabled/disabled in CarWifiHostTest

According to the bug listed,
CarWifiHostTest
#testPersistTetheringCarSetting_withCapabilityTetheringEnabled_tetheringOnReboot
is failing repeatedly remotely despite passing locally.

Looking at the new logs that were sent over via bugreport, tethering was
 never enabled initially within
 CarWifiHostTest#enablePersistTetheringAndReboot (the rest of the test
 depends on this step happening successfully, which isn't guaranteed in
 conditions like tethering not being supported)

Flag: EXEMPT bugfix
Test: atest CarWifiHostTest
Bug: 349497226
Change-Id: I997a1240d4a368c43763333a65459c837dc1a994