Code style and output improvements

Now a bit more verbose when useful.
No daemon-reload in chroot (FS#37691)
Remove CONN_DIR variable

It is not of much use.
Add option to bypass Duplicate Address Detection

After several requests, here is SkipDAD to bypass Duplicate Address
Detection.
Uniform adding and deleting of interfaces

The main benefit is the possibility to use interface hooks for links
that are created at runtime.