Fix testTetherClatBpfOffloadUdp test failure

In some cases, the test device may already have an existing CLAT
interface, causing the test to fail because it assumes no CLAT
interface exists before running the test. This change fixes the issue
by retrieving the correct test CLAT interface by its name.

Bug: 361219545
Test: atest EthernetTetheringTest#testTetherClatBpfOffloadUdp
Change-Id: Ie2cdd9c9a6fd143c8419636a448297b36f3c1c40
2 files changed