We have some slabs that the nfs4 server uses to store state objects.
We're currently creating and destroying those slabs whenever the server
is brought up or down.  That seems excessive; may as well just do that
in module initialization and exit.

Also add some minor header cleanup.  (Thanks to Andrew Morton for that
and a compile fix.)
Signed-off-by: N"J. Bruce Fields" <bfields@citi.umich.edu>
Acked-by: NNeil Brown <neilb@suse.de>