dispatcher: Not possible to deactivate probing of destination by reload

[mtryfoss]

Pre-Submission Checklist

• Commit message has the format required by CONTRIBUTING guide
• Commits are split per component (core, individual modules, libs, utils, ...)
• Each component has a single commit (if not, squash them into one commit)
• No commits to README files for modules (changes must be done to docbook files
  in doc/ subfolder, the README file is autogenerated)

Type Of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)

Checklist:

• PR should be backported to stable branches
• Tested changes locally
• Related to issue #XXXX (replace XXXX with an open issue number)

Description

If ds_probing_mode is set to 3, flag in the dispatcher entry needs to include 8
for probing to happen.

Changing a destination to not include this anymore while the destination do
not respond to OPTIONS will cause the probing flag to be re-added because of the
delayed response. A restart will fix it.

We need to check against the probing flag in the CB function to determine if
we should continue probing this destination. If probing is deativated while
waiting for a reply, we should abort.

[miconda]

Thanks!