The number of lun exposed is now exposed via sysctl by the kernel.
Use that number in ctlstat instead of the hardcoded version
Add a backward compatibility in case the sysctl(2) request fails.
This also allows ctlstat -l 1118 to actually work when having more than
1024 luns.
Reviewed by: avg, manu (both before the backward compatibility addition)
Approved by: avg, manu (both before the backward compatibility addition)
MFC after: 2 weeks
Sponsored by: Gandi.net
Differential Revision: https://reviews.freebsd.org/D13446