[collectd] Configure reporting interval on network plugin

[Marc Fournier]

Excerpts from Joel Serrano's message of 2016-02-15 20:41:58 -0800:
> 
> Has anyone successfully configured the network plugin in collectd to send
> metrics every X seconds? (like 10 seconds).

You can't control how frequently collected data is flushed to the write
target(s). Only how frequently read targets are probed.

In the case of the network plugin, the data gets flushed once its buffer
is full, which size defaults to 1.5kB. Are you collecting very little
data with a relatively high read interval ? If not you might want to
fire tcpdump to check you aren't loosing packets (remember the protocol
is UDP-based).

Note that the values dispatched include the collection time timestamp.
So even if there is some delay before they reach their final
destination, they should be stored with the correct time reference.

Cheers,
Marc