[oi-dev] docs update on NWAM

[stes@PANDORA.BE]

I've submitted a PR (pull request) for some changes for the NetWork Configuration part of the OpenIndiana System Administration handbook.

Rephrased some sentences about NWAM.

For example NWAM was described as a new approach from OpenSolaris, and that may have been true in 2008, but nowadays it does not make sense to document NWAM as something new, or to refer to OpenSolaris.  So removed that.

Also documented new things about the "sysding" service and /etc/sysding.conf for changing from Automatic to Manual mode.

I've left most of the documentation there "as it was" including the reference to nano /etc/defaultrouter,
but I've also added an example using setup_route in the /etc/sysding.conf.

Regards,
David Stes