kprobe panics with no user friendly error if device is not kprobe configured.

[datariot]

Situation
If a device is not configured as kprobe at creation time, then there are custom fields that are not associated with it in the configuration.

This will result in the error:

thread 'main' panicked at 'no entry found for key', src/custom.rs:81:26

which is not very helpful for debugging what happened. It looks like there are several tickets that have come up around this issue in the past: https://github.com/search?q=org%3Akentik+%22no+entry+found+for+key%22&type=issues.

Target
kprobe fails with an error that helps people debug the issue.

Proposal
Instead of accessing the map in a way that will cause the panic, capture an error that the field doesn't exist so the device was not setup as a kprobe device.