Temporarily add a requestNetwork flavour that takes a legacy type

This method is public @hide to support progressive refactoring of
tethering away from startUsingNetworkFeature to requestNetwork,
without getting in the way of the CONNECTIVITY_ACTION cleanup in
b/22513439 .

Bug: 9580643
Bug: 22513439
Change-Id: I9053ec746cc8f415a2d5849f044667eeb14e1b19