network: Add special case for NaN.
network: Add special case for NaN.

There are different NaN types (signaling vs. non-signaling, most notably).
collectd therefore uses a fixed representation for NaNs.

ryancox/go-collectd-travisci,wolfspyre/go-collectd,collectd/go-collectd,octo/go-collectd,ryancox/go-collectd,influxdb/go-collectd