Move MtsEthernetTetheringTest back into TetheringTest

These were originally split in two, so low-level BPF could be changed
more easily. With the introduction of MCTS, updatability of CTS tests is
not a concern anymore, so these tests can be merged back together.

Test: atest TetheringIntegrationTests
Change-Id: Ia0bd91470d445e90230f7a9546de1cb56deef9cc
2 files changed