tls_config_set_alpn
int tls_config_set_alpn(struct tls_config *_config, const char *_alpn);
if (tls_config_set_alpn(client_cfg, client_alpn) == -1)
if (tls_config_set_alpn(server_cfg, server_alpn) == -1)
if (tls_alpn != NULL && tls_config_set_alpn(tls_cfg, tls_alpn) == -1)