Add support for Network-Level security (S2 v2)

[AlCalzone]

Network Layer Security or NLS is a feature embedded within the Security 2 Command Class and provides a secure alternative for performing certain lower level mesh network protocol operations previously not addressed by S2 Security.

A SIS or Primary Controller supporting NLS MUST accept protocol commands [...] from an NLS-enabled node: only when communication is using the highest common Security Class shared between the SIS or Primary Controller and the sending node

It is currently unclear how this should work for commands the host application normally doesn't see like Assign Return Route, Set SUC ACK, etc., as S2 keys are not known to the controller atm.

Will have to wait for a Security S2 v2 capable device to test this out.