Doxygen comments for enum & structure

Added doxygen comments for enums & structures for user & channel
layers.

Unit-test:
verified build.

Change-Id: Ie5af8d6cdd4c04cb396869b7a3dc44f84efedd19
Signed-off-by: Richard Marian Thomaiyar <richard.marian.thomaiyar@linux.intel.com>
diff --git a/user_channel/channelcommands.hpp b/user_channel/channelcommands.hpp
index 84d2dcb..c612d3f 100644
--- a/user_channel/channelcommands.hpp
+++ b/user_channel/channelcommands.hpp
@@ -20,7 +20,9 @@
 namespace ipmi
 {
 
-// IPMI commands for channel command NETFN:APP.
+/**
+ * @enum IPMI commands for channel command NETFN:APP
+ */
 enum ipmi_netfn_channel_cmds
 {
     IPMI_CMD_SET_CHANNEL_ACCESS = 0x40,