MFC: r223309

MFC: r223309
Fix the kgssapi so that it can be loaded as a module. Currently
the NFS subsystems use five of the rpcsec_gss/kgssapi entry points,
but since it was not obvious which others might be useful, all
nineteen were included. Basically the nineteen entry points are
set in a structure called rpc_gss_entries and inline functions
defined in sys/rpc/rpcsec_gss.h check for the entry points being
non-NULL and then call them. A default value is returned otherwise.

git-svn-id: svn://svn.freebsd.org/base/stable/8@223748 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f