QUIC: avoid partial expansion of PATH_CHALLENGE/PATH_RESPONSE. By default packets with these frames are expanded to 1200 bytes. Previously, if anti-amplification limit did not allow this expansion, it was limited to whatever size was allowed. However RFC 9000 clearly states no partial expansion should happen in both cases. Section 8.2.1. Initiating Path Validation: An endpoint MUST expand datagrams that contain a PATH_CHALLENGE frame to at least the smallest allowed maximum datagram size of 1200 bytes, unless the anti-amplification limit for the path does not permit sending a datagram of this size. Section 8.2.2. Path Validation Responses: An endpoint MUST expand datagrams that contain a PATH_RESPONSE frame to at least the smallest allowed maximum datagram size of 1200 bytes. ... However, an endpoint MUST NOT expand the datagram containing the PATH_RESPONSE if the resulting data exceeds the anti-amplification limit.

--- a/src/event/quic/ngx_event_quic_connection.h
+++ b/src/event/quic/ngx_event_quic_connection.h
@@ -106,8 +106,7 @@ struct ngx_quic_path_s {
     size_t                            max_mtu;
     off_t                             sent;
     off_t                             received;
-    u_char                            challenge1[8];
-    u_char                            challenge2[8];
+    u_char                            challenge[2][8];
     uint64_t                          seqnum;
     uint64_t                          mtu_pnum[NGX_QUIC_PATH_RETRIES];
     ngx_str_t                         addr_text;