Include log.source.address for unparseable syslog messages

[candlerb]

Fixes #13268

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[jsoriano]

ok to test

[strawgate]

Can this move forward? This is causing us significant problems in our environment

[jsoriano]

This will need a changelog entry.

@ph could you also take a look to this change? Thanks!

[ph]

LGTM, need a changelog entry and a test

[strawgate]

Not having this is causing issues in our environment as its basically impossible to tell where the log message that is invalid came from...

[jsoriano]

@candlerb could you add the test and the changelog entry? If you don't have time it is ok, we can also continue with this change.

Thanks!

[candlerb]

Sorry, at the time I couldn't see an easy way to add a test to this without big refactoring, in a codebase I wasn't familiar with.

[jsoriano]

I am continuing with this in #15453.

@candlerb I will add you as co-author, thanks for starting with this!