tls/sni: skip SNI check if we are client

The servername_callback is also called when the server requests a
certificate in the ServerHello. However, the server will not usually
send us the server_name extension. So skip the SNI check if we are
client.

src/tls/openssl/sni.c

@@ -163,8 +163,12 @@ static int ssl_servername_handler(SSL *ssl, int *al, void *arg)
 {
 	struct tls *tls	= arg;
 	struct tls_cert *uc = NULL;
+	int ssl_state = SSL_get_state(ssl);
 	const char *sni;
 
+	if (ssl_state == TLS_ST_CR_SRVR_HELLO)
+		return SSL_TLSEXT_ERR_OK;
+
 	sni = SSL_get_servername(ssl, TLSEXT_NAMETYPE_host_name);
 	if (!str_isset(sni)) {
 		*al = SSL_AD_UNRECOGNIZED_NAME;