Update cluster config file when NOFAILOVER changes (#3280)

Currently after changing cluster-replica-no-failover, we will
call clusterUpdateMyselfFlags to trigger CLUSTER_TODO_SAVE_CONFIG.
But in gossip when the sender's NOFAILOVER changes, we won't
trigger the save, this cause nodes.conf to not save the latest
nofailover flag.

Signed-off-by: Binbin <binloveplay1314@qq.com>

src/cluster_legacy.c

@@ -4055,6 +4055,9 @@ int clusterProcessPacket(clusterLink *link) {
          * what are the instances really competing. */
         if (sender) {
             int nofailover = flags & CLUSTER_NODE_NOFAILOVER;
+            if (nofailover != clusterNodeIsNoFailover(sender)) {
+                clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG);
+            }
             sender->flags &= ~CLUSTER_NODE_NOFAILOVER;
             sender->flags |= nofailover;
         }