Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Cleanups for gcc4:

- Use socklen_t for socket functions
- Remove an unnecessary extern
- Signed/unsigned cleanups

Reviewed by: harti

Add support for the examination and modification of the devices.
This is implemented through SNMP and requires the ilmi daemon to
run on the system. To prevent bloat in rescue the atmconfig for
rescue is compiled without this stuff.