Make this c header file c++ compatible.

bacnet-stack/include/keylist.h

@@ -53,6 +53,10 @@ typedef struct Keylist {
 } KEYLIST_TYPE;
 typedef KEYLIST_TYPE *OS_Keylist;
 
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
 /* returns head of the list or NULL on failure. */
 OS_Keylist Keylist_Create(
     void);
@@ -109,4 +113,8 @@ KEY Keylist_Next_Empty_Key(
 int Keylist_Count(
     OS_Keylist list);
 
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
 #endif