Configuring port to 0 disables IP socket as specified.

This was no longer the case with 2.8 becuase of a bug introduced with
the IPv6 support. Now it is fixed.

This fixes issue #1287 and #1477.

src/redis.c

@@ -1523,7 +1523,8 @@ void initServer() {
     server.db = zmalloc(sizeof(redisDb)*server.dbnum);
 
     /* Open the TCP listening socket for the user commands. */
-    if (listenToPort(server.port,server.ipfd,&server.ipfd_count) == REDIS_ERR)
+    if (server.port != 0 &&
+        listenToPort(server.port,server.ipfd,&server.ipfd_count) == REDIS_ERR)
         exit(1);
 
     /* Open the listening Unix domain socket. */