ubus: make libubus ready for linking into C++

Use extern "C" { ... } if using libubus.h in a C++ project.

Signed-off-by: Peter Stadler <peter.stadler@student.uibk.ac.at>

libubus.h

@@ -14,6 +14,10 @@
 #ifndef __LIBUBUS_H
 #define __LIBUBUS_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #include <libubox/avl.h>
 #include <libubox/list.h>
 #include <libubox/blobmsg.h>
@@ -414,4 +418,8 @@ static inline int ubus_unregister_event_handler(struct ubus_context *ctx,
     return ubus_remove_object(ctx, &ev->obj);
 }
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif