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>
1 file changed