eth: Support looking up alternate interace channels

This makes it possible to use the GetEthDevice command to look up
interfaces other than the default NCSI interface.

Change-Id: I3a5563743a28b39adc753d8957f68f0bc330cf3a
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/handler_mock.hpp b/test/handler_mock.hpp
index edd2aec..841d986 100644
--- a/test/handler_mock.hpp
+++ b/test/handler_mock.hpp
@@ -20,7 +20,8 @@
   public:
     ~HandlerMock() = default;
 
-    MOCK_CONST_METHOD0(getEthDetails, std::tuple<std::uint8_t, std::string>());
+    MOCK_CONST_METHOD1(getEthDetails,
+                       std::tuple<std::uint8_t, std::string>(std::string));
     MOCK_CONST_METHOD1(getRxPackets, std::int64_t(const std::string&));
     MOCK_CONST_METHOD1(getCpldVersion,
                        std::tuple<std::uint8_t, std::uint8_t, std::uint8_t,