Increase rsyslog max line length

Fastly's max line length is 16k, the default rsyslog is 2k, so we are inserting a line break at 2k.

This is a problem for several lines per day when we try to process the logs with awk.

I used this as my reference: http://www.rsyslog.com/doc/rsyslog_conf_global.html I'm unsure how to test, but I can deploy and monitor it. If it were to break somehow, we have another copy of the logs going to another server for the time being.

Perhaps relevant:
Fastly say that they truncate at 16k rather than insert a line break.

/cc @dcarley