Only try to enable CK_CLYGRP if we're running on kernel newer than
1200046, the first version that supports this feature. If we set it,
then use an old kernel, we'll break the 'contract' of having
checksummed cylinder groups this flag signifies. To avoid creating
something with an inconsistent state, don't turn the flag on in these
cases. The first full fsck with a new kernel will turn this on.

Spnsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D13114