Merge changes I70384830,Ie97c2611,I7064edda,I290136b4,Ide697f65, ...

* changes:
  ethernet: add test that covers link up / down behavior
  ethernet: add updateConfiguration support to EthernetManagerTest
  ethernet: add support for enable/disableInterface in tests
  ethernet: clean up HandlerExecutor usage in test
  ethernet: address test review comments
  ethernet: get MTU size directly from TestNetworkInterface