Add api to fetch short conn id len from a given channel/tserver

Need an api to fetch the configured conn id len for short headers, add
that in here

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26592)

include/internal/quic_channel.h

@@ -313,6 +313,9 @@ OSSL_STATM *ossl_quic_channel_get_statm(QUIC_CHANNEL *ch);
 /* Gets the TLS handshake layer used with the channel. */
 SSL *ossl_quic_channel_get0_tls(QUIC_CHANNEL *ch);
 
+/* Gets the channels short header connection id length */
+size_t ossl_quic_channel_get_short_header_conn_id_len(QUIC_CHANNEL *ch);
+
 /*
  * Gets/sets the current peer address. Generally this should be used before
  * starting a channel in client mode.

include/internal/quic_record_rx.h

@@ -67,6 +67,11 @@ void ossl_qrx_set_msg_callback(OSSL_QRX *qrx, ossl_msg_cb msg_callback,
 void ossl_qrx_set_msg_callback_arg(OSSL_QRX *qrx,
                                    void *msg_callback_arg);
 
+/*
+ * Get the short header connection id len from this qrx
+ */
+size_t ossl_qrx_get_short_hdr_conn_id_len(OSSL_QRX *qrx);
+
 /*
  * Secret Management
  * =================

include/internal/quic_tserver.h

@@ -81,6 +81,9 @@ ossl_quic_tserver_get_terminate_cause(const QUIC_TSERVER *srv);
 /* Returns 1 if the server is in a terminated state */
 int ossl_quic_tserver_is_terminated(const QUIC_TSERVER *srv);
 
+/* Get out short header conn id length */
+size_t ossl_quic_tserver_get_short_header_conn_id_len(const QUIC_TSERVER *srv);
+
 /*
  * Attempts to read from stream 0. Writes the number of bytes read to
  * *bytes_read and returns 1 on success. If no bytes are available, 0 is written