Add configuration object and builder for creating tun/tap interfaces

This change is finally (!) adding a builder class for creating tun/tap
interfaces for testing.

The various create*Interface() methods which are not marked as
@SystemApi can be removed after moving existing tests over to the new
API.

Bug: 237694424
Test: TH
Change-Id: I10eff755ebda4e2ef2550a50a3bfd1543a21e5b0
1 file changed