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/usercommands.cpp b/user_channel/usercommands.cpp
index f81c093..b0997d5 100644
--- a/user_channel/usercommands.cpp
+++ b/user_channel/usercommands.cpp
@@ -37,6 +37,10 @@
 static constexpr uint8_t setPassword = 0x02;
 static constexpr uint8_t testPassword = 0x03;
 
+/** @struct SetUserAccessReq
+ *
+ *  Structure for set user access request command (refer spec sec 22.26)
+ */
 struct SetUserAccessReq
 {
 #if BYTE_ORDER == LITTLE_ENDIAN
@@ -68,6 +72,10 @@
 
 } __attribute__((packed));
 
+/** @struct GetUserAccessReq
+ *
+ *  Structure for get user access request command (refer spec sec 22.27)
+ */
 struct GetUserAccessReq
 {
 #if BYTE_ORDER == LITTLE_ENDIAN
@@ -84,6 +92,10 @@
 #endif
 } __attribute__((packed));
 
+/** @struct GetUserAccessResp
+ *
+ *  Structure for get user access response command (refer spec sec 22.27)
+ */
 struct GetUserAccessResp
 {
 #if BYTE_ORDER == LITTLE_ENDIAN
@@ -105,6 +117,10 @@
     PrivAccess privAccess;
 } __attribute__((packed));
 
+/** @struct SetUserNameReq
+ *
+ *  Structure for set user name request command (refer spec sec 22.28)
+ */
 struct SetUserNameReq
 {
 #if BYTE_ORDER == LITTLE_ENDIAN
@@ -118,6 +134,10 @@
     uint8_t userName[16];
 } __attribute__((packed));
 
+/** @struct GetUserNameReq
+ *
+ *  Structure for get user name request command (refer spec sec 22.29)
+ */
 struct GetUserNameReq
 {
 #if BYTE_ORDER == LITTLE_ENDIAN
@@ -130,11 +150,19 @@
 #endif
 } __attribute__((packed));
 
+/** @struct GetUserNameResp
+ *
+ *  Structure for get user name response command (refer spec sec 22.29)
+ */
 struct GetUserNameResp
 {
     uint8_t userName[16];
 } __attribute__((packed));
 
+/** @struct SetUserPasswordReq
+ *
+ *  Structure for set user password request command (refer spec sec 22.30)
+ */
 struct SetUserPasswordReq
 {
 #if BYTE_ORDER == LITTLE_ENDIAN