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/handler.hpp b/handler.hpp
index f4b1bbd..fdb2585 100644
--- a/handler.hpp
+++ b/handler.hpp
@@ -24,7 +24,8 @@
      *
      * @return tuple of ethernet details (channel, if name).
      */
-    virtual std::tuple<std::uint8_t, std::string> getEthDetails() const = 0;
+    virtual std::tuple<std::uint8_t, std::string>
+        getEthDetails(std::string intf) const = 0;
 
     /**
      * Return the value of rx_packets, given a if_name.