Narrow the effects of PR #6029 to the exact state.

CLIENT PAUSE may be used, in other contexts, for a long time making all
the slaves time out. Better for now to be more specific about what
should disable senidng PINGs.

An alternative to that would be to virtually refresh the slave
interactions when clients are paused, however for now I went for this
more conservative solution.

src/replication.c

@@ -30,6 +30,7 @@
 
 
 #include "server.h"
+#include "cluster.h"
 
 #include <sys/time.h>
 #include <unistd.h>
@@ -2601,12 +2602,23 @@ void replicationCron(void) {
 
     /* First, send PING according to ping_slave_period. */
     if ((replication_cron_loops % server.repl_ping_slave_period) == 0 &&
-        listLength(server.slaves) && !clientsArePaused())
+        listLength(server.slaves))
     {
-        ping_argv[0] = createStringObject("PING",4);
-        replicationFeedSlaves(server.slaves, server.slaveseldb,
-            ping_argv, 1);
-        decrRefCount(ping_argv[0]);
+        /* Note that we don't send the PING if the clients are paused during
+         * a Redis Cluster manual failover: the PING we send will otherwise
+         * alter the replication offsets of master and slave, and will no longer
+         * match the one stored into 'mf_master_offset' state. */
+        int manual_failover_in_progress =
+            server.cluster_enabled &&
+            server.cluster->mf_end &&
+            clientsArePaused();
+
+        if (!manual_failover_in_progress) {
+            ping_argv[0] = createStringObject("PING",4);
+            replicationFeedSlaves(server.slaves, server.slaveseldb,
+                ping_argv, 1);
+            decrRefCount(ping_argv[0]);
+        }
     }
 
     /* Second, send a newline to all the slaves in pre-synchronization