server: bump listen() backlog With the default if 0, we trigger a lot of these: [29055.817884] TCP: request_sock_TCP: Possible SYN flooding on port 8765. Sending cookies. Check SNMP counters. Set it to 4, even 2 seems to be enough to get rid of it. Signed-off-by: Jens Axboe <axboe@fb.com>