Tests just need a specifier to verify general NetworkSpecifier
functionality. They can use EthernetNetworkSpecifier the same way they
use StringNetworkSpecifier.
To keep the tests passing on Q and R, add a CompatUtil class that will
keep creating StringNetworkSpecifiers (now removed) instead.
Bug: 179329291
Test: atest CtsNetTestCases
(note the merged-in clause is an unrelated change, used to avoid the
branch)
Merged-In: I8a6d7cf41c4bbc61cee1bb5570cee5bbeb85be49
Change-Id: Ic6bf611ba36b555e4e0bb1bd3fa0053fe29dc8cf
de9dbf5b3c