Reuse UDP socket while flushing stats

[ljank]

Otherwise after each flush total process connection count is constantly increasing and is never cleaned up:

$ ps aux | grep statsd
statsd   29807 38.3  0.0 1253624 35228 ?       Ssl  10:58   8:46 statsd /opt/statsd/config_buffering_repeater.js
$ lsof -p 29807 | wc -l
1423
$ lsof -p 29807 | tail -n 10
statsd  29807 statsd 1383u     IPv4         1586135868      0t0        UDP *:40056
statsd  29807 statsd 1384u     IPv4         1586147589      0t0        UDP *:55934
statsd  29807 statsd 1385u     IPv4         1586135879      0t0        UDP *:45790
statsd  29807 statsd 1386u     IPv4         1586146873      0t0        UDP *:37203
statsd  29807 statsd 1387u     IPv4         1586150537      0t0        UDP *:49581
statsd  29807 statsd 1388u     IPv4         1586146884      0t0        UDP *:33677
statsd  29807 statsd 1389u     IPv4         1586146885      0t0        UDP *:59865
statsd  29807 statsd 1390u     IPv4         1586150558      0t0        UDP *:42280
statsd  29807 statsd 1391u     IPv4         1586150575      0t0        UDP *:45595
statsd  29807 statsd 1392u     IPv4         1586149498      0t0        UDP *:45977

@obradovic