[master] correct the maximum NTA lifetime in rndc's help output
[master] correct the maximum NTA lifetime in rndc's help output

pecharmin/bind9,each/bind9-collab,pecharmin/bind9,each/bind9-collab,pecharmin/bind9,each/bind9-collab,each/bind9-collab,pecharmin/bind9,pecharmin/bind9,pecharmin/bind9,each/bind9-collab,each/bind9-collab