logs: prevent multiple warnings

ccminer.cpp

@@ -555,7 +555,7 @@ static int share_result(int result, const char *reason)
 			applog(LOG_WARNING, "factor reduced to : %0.2f", opt_difficulty);
 			return 0;
 		}
-		if (strncmp(reason, "Duplicate share", 15) == 0) {
+		if (strncmp(reason, "Duplicate share", 15) == 0 && !check_dups) {
 			applog(LOG_WARNING, "enabling duplicates check feature");
 			check_dups = true;
 		}

util.cpp

@@ -1287,9 +1287,10 @@ static bool stratum_set_difficulty(struct stratum_ctx *sctx, json_t *params)
 	pthread_mutex_unlock(&sctx->work_lock);
 
 	/* store for api stats */
+	if (diff != global_diff) {
 		global_diff = diff;
-
 		applog(LOG_WARNING, "Stratum difficulty set to %g", diff);
+	}
 
 	return true;
 }