TCP Keepalive in curl is only in very recent versions and not required with regular messages on stratum anyway.
diff --git a/util.c b/util.c
index 7d7ca43..17e2428 100644
--- a/util.c
+++ b/util.c
@@ -1236,7 +1236,6 @@ bool initiate_stratum(struct pool *pool)
curl_easy_setopt(curl, CURLOPT_URL, s);
curl_easy_setopt(curl, CURLOPT_TCP_NODELAY, 1);
curl_easy_setopt(curl, CURLOPT_USE_SSL, CURLUSESSL_TRY);
- curl_easy_setopt(curl, CURLOPT_TCP_KEEPALIVE, 1);
if (pool->rpc_proxy) {
curl_easy_setopt(curl, CURLOPT_PROXY, pool->rpc_proxy);
curl_easy_setopt(curl, CURLOPT_PROXYTYPE, pool->rpc_proxytype);