Fix #245, use type safe value for CFE_SB_MsgId_t

This makes CFE_SB_MsgId_t to be a safe wrapper around CFE_SB_MsgId_Atom_t,
such that the values cannot be silently/implicitly interchanged with other
integers.

This enforces that the MsgId/Value conversion helpers must be used when
conversion to/from integers is intended.

modules/core_api/fsw/inc/cfe_sb_api_typedefs.h

@@ -63,7 +63,10 @@
  *
  * \sa CFE_SB_ValueToMsgId()
  */
-#define CFE_SB_MSGID_WRAP_VALUE(val) (val)
+#define CFE_SB_MSGID_WRAP_VALUE(val) \
+    {                                \
+        val                          \
+    }
 
 /**
  * \brief Translation macro to convert to MsgId integer values from a literal
@@ -88,7 +91,7 @@
  *
  * \sa CFE_SB_MsgIdToValue()
  */
-#define CFE_SB_MSGID_UNWRAP_VALUE(mid) ((CFE_SB_MsgId_Atom_t)(mid))
+#define CFE_SB_MSGID_UNWRAP_VALUE(mid) ((mid).Value)
 
 /**
  * \brief Reserved value for CFE_SB_MsgId_t that will not match any valid MsgId

modules/core_api/fsw/inc/cfe_sb_extern_typedefs.h

@@ -115,7 +115,10 @@ typedef uint32 CFE_SB_MsgId_Atom_t;
  * @note In a future version it could become a type-safe wrapper similar to the route index,
  * to avoid message IDs getting mixed between other integer values.
  */
-typedef CFE_SB_MsgId_Atom_t CFE_SB_MsgId_t;
+typedef struct
+{
+    CFE_SB_MsgId_Atom_t Value;
+} CFE_SB_MsgId_t;
 
 /** \brief  CFE_SB_PipeId_t to primitive type definition
  *