Disable tuning large for BIND 9.16

In BIND 9.16, the settings enabled by --with-tuning=large has been enabled by default. Those setting prefer performance over memory consumption. As the BIND 9.16 conversion to netmgr wasn't complete the extra memory consumption is amplified by memory fragmentation in the default system allocator.

It would be safe thing to do to disable the tuning large for BIND 9.16 and keep it enabled for BIND 9.18 - almost all of those settings are now gone in 9.18+ and named now uses jemalloc memory allocator which is much better at handling memory fragmentation (matching our workloads).