[PATCH] nfsd4: slabify nfs4_files

The structures the server uses to keep track of various pieces of nfsv4 state
(open files, outstanding delegations, etc.) are likely to be allocated and
deallocated frequently and seem reasonable candidates for slab caches.

While we're at it, the slab code keeps statistics that help catch leaks and
such, so we may as well take this chance to eliminate some debugging counters
that we've been keeping ourselves.

Start with the struct nfs4_file.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>