Use a more restricted range of supported __FreeBSD_version values for
the virtualbox kernel module since it uses internal KPIs for which KBI
stability is not guaranteed. DECLARE_MODULE_TIED would tie the module
to a specific __FreeBSD_version which would cause the module to stop
loading when an SA or EN is pushed on a release branch. Instead, use
DECLARE_MODULE_MAXVER with an upper bound that is limited to the range
of a releng branch so that a module built on X.Y will load on X.Y with
SAs or ENs applied but will fail to load on X.Y-1 or X.Y+1.
Reviewed by: kevans, imp, madpilot, lwhsu (earlier version)
Differential Revision: https://reviews.freebsd.org/D16119
bc6d5725ed