Use correct final reference counter value for 9.11 and 9.16
With the commit 542096278ba605a5800348a6c31dc058685860de, reference
counting uses C11 semantics due to
bind-9.16: Correct reference counting
With [0] BIND atomic functions for reference counting have the
identical interface as their C11 counter parts. This means that
these functions return the _previous_ refcount instead of the
current one.
[0]: https://gitlab.isc.org/isc-projects/bind9/-/commit/bef8ac5bae0f95dbff76ec99a7994024a5d6c64e
Since the same code is compiled for both 9.11 and 9.16, we need to make
sure the logic to detect final reference counter value in destructors
follows two different reference counting interface semantics.
Define REFCOUNT_FLOOR to help with that depending on the libdns major
version.
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1899744
Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>