For being able to use e.g. "-v" to use TCP communication with the NSUPDATE_SERVER -> NSUPDATE_OPT has been added.
NSUPDATE_OPT will be plainly added to the command line of nsupdate.
NSUPDATE_OPT will also be saved to conf respectively read from conf
The current script is already broken due to Bind 9.16 -> 9.18 changes
due to their renaming scheme for primary/secondary so do not rely on the
compat layer (which was also broken for other reasons).