Cluster: initialized not used fileds in gossip section.

Otherwise we risk sending not initialized data to other nodes, that may
contain anything. This was actually not possible only because the
initialization of the buffer where the cluster packets header is created
was larger than the 3 gossip sections we use, so the memory was already
all filled with zeroes by the memset().

src/cluster.c

@@ -2195,6 +2195,8 @@ void clusterSendPing(clusterLink *link, int type) {
         memcpy(gossip->ip,this->ip,sizeof(this->ip));
         gossip->port = htons(this->port);
         gossip->flags = htons(this->flags);
+        gossip->notused1 = 0;
+        gossip->notused2 = 0;
         gossipcount++;
     }