Apply immediately the first set_difficulty

This is a workaround for pool, who send the first difficulty after notify

util.c

@@ -2008,7 +2008,9 @@ static bool parse_notify(struct pool *pool, json_t *val)
 	snprintf(pool->nbit, 9, "%s", nbit);
 	snprintf(pool->ntime, 9, "%s", ntime);
 	pool->swork.clean = clean;
-	pool->sdiff = pool->next_diff;
+	if (pool->next_diff > 0) {
+		pool->sdiff = pool->next_diff;
+	}
 	alloc_len = pool->coinbase_len = cb1_len + pool->n1_len + pool->n2size + cb2_len;
 	pool->nonce2_offset = cb1_len + pool->n1_len;
 
@@ -2117,8 +2119,13 @@ static bool parse_diff(struct pool *pool, json_t *val)
 		return false;
 
 	cg_wlock(&pool->data_lock);
-	old_diff = pool->next_diff;
-	pool->next_diff = diff;
+	if (pool->next_diff > 0) {
+		old_diff = pool->next_diff;
+		pool->next_diff = diff;
+	} else {
+		old_diff = pool->sdiff;
+		pool->next_diff = pool->sdiff = diff;
+	}
 	cg_wunlock(&pool->data_lock);
 
 	if (old_diff != diff) {
@@ -2916,7 +2923,8 @@ bool initiate_stratum(struct pool *pool)
 		if (!pool->stratum_url)
 			pool->stratum_url = pool->sockaddr_url;
 		pool->stratum_active = true;
-		pool->next_diff = pool->sdiff = 1;
+		pool->next_diff = 0;
+		pool->sdiff = 1;
 		if (opt_protocol) {
 			applog(LOG_DEBUG, "Pool %d confirmed mining.subscribe with extranonce1 %s extran2size %d",
 			       pool->pool_no, pool->nonce1, pool->n2size);