MINOR: connection: add conn_stop_tracking() to disable tracking

This will be used before conn_full_close() instead of using
conn_force_close(), resulting in a clearer exit path in various
situations.
diff --git a/include/proto/connection.h b/include/proto/connection.h
index dd19714..7fdee7c 100644
--- a/include/proto/connection.h
+++ b/include/proto/connection.h
@@ -142,6 +142,14 @@
 	conn_ctrl_close(conn);
 }
 
+/* stop tracking a connection, allowing conn_full_close() to always
+ * succeed.
+ */
+static inline void conn_stop_tracking(struct connection *conn)
+{
+	conn->flags &= ~CO_FL_XPRT_TRACKED;
+}
+
 /* Force to close the connection whatever the tracking state. This is mainly
  * used on the error path where the tracking does not make sense, or to kill
  * an idle connection we want to abort immediately.