split out handler implementation from interface

Split out the handler object definition from the interface and drop the
default parameters.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: Ie8c9dbf7881bbe6b5af3596a60430e3b3d573762
diff --git a/cable.hpp b/cable.hpp
index 6e559c0..58b82ce 100644
--- a/cable.hpp
+++ b/cable.hpp
@@ -19,7 +19,7 @@
 // Handle the cablecheck.  Sys must supply which ethernet device they're
 // interested in.
 ipmi_ret_t cableCheck(const uint8_t* reqBuf, uint8_t* replyBuf, size_t* dataLen,
-                      const HandlerInterface* handler = &handlerImpl);
+                      const HandlerInterface* handler);
 
 } // namespace ipmi
 } // namespace google