network_settings/vpn: Make add-on more generic.

networking: Hostname viewing & setting

addon/network settings/hostname

allowing the hostname for the system to be set by the user using
the preferences gui

Change-Id: I676c368070ef89a20435f97ee39e3caa25abf8f9
Reviewed-on: https://review.haiku-os.org/c/870
Reviewed-by: Axel Dörfler <axeld@pinc-software.de>
Reviewed-by: Stephan Aßmus <superstippi@gmx.de>

network_settings/Jamfile: Add dialup SubInclude.

(Still not included in the build, of course.)

network preflet: Introduce early OpenVPN add-on

* Not included in image... will likely be quite some
time until it is :-)

Network: beginnings of the DNS settings.

Network: added telnet and ftp service add-ons.

* They're old, but we still have them on our image.

Network: first steps to an SSH service add-on.

Network: Added IPv6Interface.

* Pretty much the same as the IPv4 one.

Added IPv4Interface add-on for Network preferences.

* Took over most code from the former InterfacesAddOn, and
moved it to where it should be.
* However, it doesn't work yet at all.

Network: beginnings of the DNS settings.

Network: added telnet and ftp service add-ons.

* They're old, but we still have them on our image.

Network: first steps to an SSH service add-on.

Network: Added IPv6Interface.

* Pretty much the same as the IPv4 one.

Added IPv4Interface add-on for Network preferences.

* Took over most code from the former InterfacesAddOn, and
moved it to where it should be.
* However, it doesn't work yet at all.