manner analogous to r216633 for the regular server. This
change busies the file system so that VFS_VGET() is
guaranteed to be using the correct mount point even
during a forced dismount attempt. Since nfsd_fhtovp() is
not called immediately before readdirplus, the patch is
actually a clone of pjd@'s nfs_serv.c.4.patch instead of
the one committed in r216633.
Reviewed by: kib
MFC after: 10 days
f9266eb1f9