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/common.cpp b/test/common.cpp
index 08c3eaa..f8f635f 100644
--- a/test/common.cpp
+++ b/test/common.cpp
@@ -3,8 +3,8 @@
 
 namespace ipmi
 {
-std::uint8_t getChannelByName(const std::string&)
+std::uint8_t getChannelByName(const std::string& chName)
 {
-    return 1;
+    return chName.size() + 10;
 }
 } // namespace ipmi