[nrf fromlist] net: sockets: tls: Allow SNI extension for DTLS

DTLS systems can accept the Server Name Indication extension
without using X509 certificates.  Allow this for either
MBEDTLS_X509_CRT_PARSE_C or CONFIG_MBEDTLS_DTLS.

Upstream PR: zephyrproject-rtos/zephyr#44914

Signed-off-by: Pete Skeggs <peter.skeggs@nordicsemi.no>

subsys/net/lib/sockets/sockets_tls.c

@@ -459,7 +459,7 @@ static struct tls_context *tls_clone(struct tls_context *source_tls)
 	memcpy(&target_tls->options, &source_tls->options,
 	       sizeof(target_tls->options));
 
-#if defined(MBEDTLS_X509_CRT_PARSE_C)
+#if defined(MBEDTLS_X509_CRT_PARSE_C) || defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
 	if (target_tls->options.is_hostname_set) {
 		mbedtls_ssl_set_hostname(&target_tls->ssl,
 					 source_tls->ssl.hostname);
@@ -1262,7 +1262,7 @@ static int tls_mbedtls_init(struct tls_context *context, bool is_server)
 	}
 #endif /* CONFIG_NET_SOCKETS_ENABLE_DTLS */
 
-#if defined(MBEDTLS_X509_CRT_PARSE_C)
+#if defined(MBEDTLS_X509_CRT_PARSE_C) || defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
 	/* For TLS clients, set hostname to empty string to enforce it's
 	 * verification - only if hostname option was not set. Otherwise
 	 * depend on user configuration.
@@ -1403,7 +1403,7 @@ static int tls_opt_hostname_set(struct tls_context *context,
 {
 	ARG_UNUSED(optlen);
 
-#if defined(MBEDTLS_X509_CRT_PARSE_C)
+#if defined(MBEDTLS_X509_CRT_PARSE_C) || defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
 	if (mbedtls_ssl_set_hostname(&context->ssl, optval) != 0) {
 		return -EINVAL;
 	}