Feature/bpf management improvements

Improvements to how the BPF management salt state gets a list of the interfaces on the machine that it will manage. This will now assume that all of the interface configuration files have been created, if they haven't, the user will have to create a `sensor_interfaces` grain.

In the future it might be best to populate the `sensor_interfaces` grain with a custom grain to parse `/etc/nsm/sensortab` to have a list of enabled sensor interfaces available to Salt states.