MEDIUM: applets: Use the new _HA_ATOMIC_* macros.

Use the new _HA_ATOMIC_* macros and add barriers where needed.
diff --git a/include/proto/applet.h b/include/proto/applet.h
index d664fd9..efcc525 100644
--- a/include/proto/applet.h
+++ b/include/proto/applet.h
@@ -75,7 +75,7 @@
 		LIST_INIT(&appctx->buffer_wait.list);
 		appctx->buffer_wait.target = appctx;
 		appctx->buffer_wait.wakeup_cb = appctx_buf_available;
-		HA_ATOMIC_ADD(&nb_applets, 1);
+		_HA_ATOMIC_ADD(&nb_applets, 1);
 	}
 	return appctx;
 }
@@ -95,7 +95,7 @@
 	}
 
 	pool_free(pool_head_connection, appctx);
-	HA_ATOMIC_SUB(&nb_applets, 1);
+	_HA_ATOMIC_SUB(&nb_applets, 1);
 }
 
 static inline void appctx_free(struct appctx *appctx)