QUIC: fixed handling of RETIRE_CONNECTION_ID frame. Previously, the retired socket was not closed if it didn't match active or backup. New sockets could not be created (due to count limit), since retired socket was not closed before calling ngx_quic_create_sockets(). When replacing retired socket, new socket is only requested after closing old one, to avoid hitting the limit on the number of active connection ids. Together with added restrictions, this fixes an issue when a current socket could be closed during migration, recreated and erroneously reused leading to null pointer dereference.

--- a/src/event/quic/ngx_event_quic_socket.h
+++ b/src/event/quic/ngx_event_quic_socket.h
@@ -22,6 +22,7 @@ ngx_int_t ngx_quic_listen(ngx_connection
     ngx_quic_socket_t *qsock);
 void ngx_quic_close_socket(ngx_connection_t *c, ngx_quic_socket_t *qsock);
 
+void ngx_quic_unref_path(ngx_connection_t *c, ngx_quic_path_t *path);
 void ngx_quic_connect(ngx_connection_t *c, ngx_quic_socket_t *qsock,
     ngx_quic_path_t *path, ngx_quic_client_id_t *cid);