QUIC: stream flow control refactored. - Function ngx_quic_control_flow() is introduced. This functions does both MAX_DATA and MAX_STREAM_DATA flow controls. The function is called from STREAM and RESET_STREAM frame handlers. Previously, flow control was only accounted for STREAM. Also, MAX_DATA flow control was not accounted at all. - Function ngx_quic_update_flow() is introduced. This function advances flow control windows and sends MAX_DATA/MAX_STREAM_DATA. The function is called from RESET_STREAM frame handler, stream cleanup handler and stream recv() handler.

--- a/src/event/quic/ngx_event_quic.h
+++ b/src/event/quic/ngx_event_quic.h
@@ -75,6 +75,7 @@ struct ngx_quic_stream_s {
     uint64_t                   send_max_data;
     uint64_t                   recv_max_data;
     uint64_t                   recv_offset;
+    uint64_t                   recv_window;
     uint64_t                   recv_last;
     uint64_t                   final_size;
     ngx_chain_t               *in;