Cluster: fix gossip section ping/pong times encoding.

The gossip section times are 32 bit, so cannot store the milliseconds
time but just the seconds approximation, which is good enough for our
uses. At the same time however, when comparing the gossip section times
of other nodes with our node's view, we need to convert back to
milliseconds.

Related to redis#3929. Without this change the patch to reduce the traffic in
the bus message does not work.

src/cluster.c

@@ -1362,7 +1362,8 @@ void clusterProcessGossipSection(clusterMsg *hdr, clusterLink *link) {
                 node->ping_sent == 0 &&
                 clusterNodeFailureReportsCount(node) == 0)
             {
-                uint32_t pongtime = ntohl(g->pong_received);
+                mstime_t pongtime = ntohl(g->pong_received);
+                pongtime *= 1000; /* Convert back to milliseconds. */
                 if (pongtime > node->pong_received) {
                     node->pong_received = pongtime;
                 }
@@ -2353,8 +2354,8 @@ void clusterSendPing(clusterLink *link, int type) {
         freshnodes--;
         gossip = &(hdr->data.ping.gossip[gossipcount]);
         memcpy(gossip->nodename,this->name,CLUSTER_NAMELEN);
-        gossip->ping_sent = htonl(this->ping_sent);
-        gossip->pong_received = htonl(this->pong_received);
+        gossip->ping_sent = htonl(this->ping_sent/1000);
+        gossip->pong_received = htonl(this->pong_received/1000);
         memcpy(gossip->ip,this->ip,sizeof(this->ip));
         gossip->port = htons(this->port);
         gossip->cport = htons(this->cport);