EthernetManagerTest: update tests that bring up tap without carrier

The old way to bring up a tap interface without carrier was flaky. So
update the tests in line with TestNetworkService changes that start
using IFF_NO_CARRIER to configure an interface without carrier.

Test: atest EthernetManagerTest
Bug: 249611919
Change-Id: I33bc80cc03a92887a79bffaa7a5bf38b0e66b3a7
1 file changed