Rename APIs in NetworkAgentConfig.Builder

As API review feedback, rename disableProvisioningNotification()
to setEnabledProvisioningNotification and disableNat64Detection()
to setEnabledNat64Detection. Also, update code in caller side
accordingly.

Bug: 184735772
Test: make update-api ; atest FrameworksNetTests
Change-Id: If7305634863d1503c967e5593ebd0c8af2174bea