move implementation to ipmi file

Move the entrance point for the IPMI OEM handling to a separate file and
pass in the handler pointer via binding.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I4371ebee1c252ab6e9d8a7ff2389583919ecc996
diff --git a/eth.cpp b/eth.cpp
index 2d21c57..2b38939 100644
--- a/eth.cpp
+++ b/eth.cpp
@@ -17,7 +17,7 @@
 #include "eth.hpp"
 
 #include "handler.hpp"
-#include "main.hpp"
+#include "ipmi.hpp"
 
 #include <cstdint>
 #include <cstring>