Remove the NATM framework including the en(4), fatm(4), hatm(4), and

Remove the NATM framework including the en(4), fatm(4), hatm(4), and
patm(4) devices.

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 (some newer devices that patm(4) could be updated to
support apparently exist, but we do not currently have support).

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.

Note well: FreeBSD 11 supports NATM and will continue to do so until at
least September 30, 2021.  Improvements to the code in FreeBSD 11 are
certainly welcome.

Reviewed by:	philip
Approved by:	harti