Maintaining an address family and framework has real costs when we make
infrastructure improvements. In the case of NATM we support no devices
manufactured in the last 20 years and some will not even work in modern
motherboards.
With this change, support remains for some netgraph modules that don't
require NATM support code. It is unclear if all these should remain,
though ng_atmllc certainly stands alone.
The mbpool(9) framework will be removed in a seperate commit.