NetFn: Use api.hpp instead of api.h

Since NetFn declared in api.h has been gradually deprecated, this
submission is to use api.hpp instead of api.h.

https://gerrit.openbmc.org/c/openbmc/phosphor-host-ipmid/+/79391

Change-Id: I7e16e96b716d0483c4137801ab7bdaf19fa0738b
Signed-off-by: George Liu <liuxiwei@ieisystem.com>
diff --git a/hiomap.cpp b/hiomap.cpp
index 9c2e8cd..b42c4c1 100644
--- a/hiomap.cpp
+++ b/hiomap.cpp
@@ -854,6 +854,6 @@
         };
     registerSignalHandler(ipmi::prioMax, SIGTERM, shutdownHandler);
 
-    ipmi_register_callback(NETFUN_IBM_OEM, IPMI_CMD_HIOMAP, ctx,
+    ipmi_register_callback(ipmi::netFnOemSix, IPMI_CMD_HIOMAP, ctx,
                            openpower::flash::hiomap_dispatch, SYSTEM_INTERFACE);
 }