Redis genRedisInfoString repl_down_since of struct redisServer is wrong when slave never connect to master success

When master and slave both come down then slave start again. the slave never connect master success and server.repl_down_since is 0. genRedisInfoString repl_down_since send to sentinel is server.unixtime actual. So sentinel consinder the slave link down to master too long and don't promoted it.

        if (server.repl_state != REPL_STATE_CONNECTED) {
            info = sdscatprintf(info,
                "master_link_down_since_seconds:%jd\r\n",
                (intmax_t)(server.unixtime-server.repl_down_since));
        }

Comment From: z00526391

It should be designed in this way. When slave restarted it never connected to master, can't tell how much difference with master, and don't promoted it to master.