Call psa_crypto_init in the library when required for TLS 1.3

For backward compatibility with Mbed TLS <=3.5.x, applications must be able
to make a TLS connection with a peer that supports both TLS 1.2 and TLS 1.3,
regardless of whether they call psa_crypto_init(). Since Mbed TLS 3.6.0,
we enable TLS 1.3 in the default configuration, so we must take care of
calling psa_crypto_init() if needed. This is a change from TLS 1.3 in
previous versions, where enabling MBEDTLS_SSL_PROTO_TLS1_3 was a user
choice and could have additional requirement.

This commit makes the library call psa_crypto_init() when it needs PSA
crypto in a situation where the application might not have called it,
namely, when starting a TLS 1.3 connection.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

library/ssl_tls13_server.c

@@ -1948,6 +1948,11 @@ static int ssl_tls13_process_client_hello(mbedtls_ssl_context *ssl)
 
     MBEDTLS_SSL_DEBUG_MSG(2, ("=> parse client hello"));
 
+    ret = mbedtls_ssl_tls13_crypto_init(ssl);
+    if (ret != 0) {
+        return ret;
+    }
+
     MBEDTLS_SSL_PROC_CHK(mbedtls_ssl_tls13_fetch_handshake_msg(
                              ssl, MBEDTLS_SSL_HS_CLIENT_HELLO,
                              &buf, &buflen));