Added generation of CC frames with error on connection termination. When an error occurs, then c->quic->error field may be populated with an appropriate error code, and the CONNECTION CLOSE frame will be sent to the peer before the connection is closed. Otherwise, the error treated as internal and INTERNAL_ERROR code is sent. The pkt->error field is populated by functions processing packets to indicate an error when it does not fit into pass/fail return status.

--- a/src/event/ngx_event_quic_transport.h
+++ b/src/event/ngx_event_quic_transport.h
@@ -278,6 +278,7 @@ typedef struct {
     uint32_t                                    version;
     ngx_str_t                                   token;
     enum ssl_encryption_level_t                 level;
+    ngx_uint_t                                  error;
 
     /* filled in by parser */
     ngx_buf_t                                  *raw;   /* udp datagram */