Internal plugin increases size of reported buffer limit on reload

[danielnelson]

Bug report

Each time Telegraf is reloaded the internal_write buffer_limit field is incremented by the buffer limit.

Relevant telegraf.conf:

System info:

telegraf 1.5.2

Steps to reproduce:

1. enable internal plugin
2. start telegraf
3. reload telegraf with sighup

Expected behavior:

buffer_limit remains the same

Actual behavior:

buffer_limit is incremented

[danielnelson]

8147d60