[2430] Use $GENERATE in NS records too

tests/lettuce/data/generate.zone

@@ -1,6 +1,4 @@
 $ORIGIN example.org.
-example.org.	3600	IN	SOA	ns1.example.org. admin.example.org. 12341 3600 1800 2419200 7200
-example.org.	3600	IN	NS	ns1.example.org.
-example.org.	3600	IN	NS	ns2.example.org.
-
+example.org.    3600    IN      SOA     ns1.example.org. admin.example.org. 12341 3600 1800 2419200 7200
+$GENERATE 1-2   @               NS      ns$.example.org.
 $GENERATE 1-4 host$ A 192.0.2.$