[nsd-users] fix for allow-axfr-fallback man page entry

[Paul Wouters]

[ Would have sent patch if man pages were not maintained in nroff ]

The man page entry in nsd.conf for allow-axfr-fallback does not list
the default value. Looking at the code, the default value is one. I
suggest adding to the section:

 	The default is to allow axfr fallback.

Paul
ps. see doclifter to do nroff->xml and xmlto to do xml->nroff