oob: Refactor oob callback handling and move it to adapter code

oob: Refactor oob callback handling and move it to adapter code

This allows oob plugin to register for callback after executing
certain action on adapter. Currently reading local OOB data and
pairing is supported. It should be easy to support more callbacks
in future if needed e.g. powering on.

Thanks to this plugin is not required to duplicate code that would
validate adapter/device when callback is received as callback condition
is check in adapter.

It also allows to pass user data which will be provided back when cb
is called further reducing plugin code.