sys: net: Initial import of a simple data-forwarding MAC protocol (nomac)

This is basically an adapter translating `netapi` IPC calls into `netdev` function calls.

Depends on ~~#1448~~ (merged) and ~~#2027~~ (merged)
Might be, that even my driver implementations are wrong ^^" this sequence of events crystallized only very recently (compared to the model in general).