knfsd: nfsd4: don't delegate files that have had conflicts

One more incremental delegation policy improvement: don't give out a
delegation on a file if conflicting access has previously required that a
delegation be revoked on that file.  (In practice we'll forget about the
conflict when the struct nfs4_file is removed on close, so this is of limited
use for now, though it should at least solve a temporary problem with
self-conflicts on write opens from the same client.)

Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/nfsd/state.h

@@ -224,6 +224,7 @@ struct nfs4_file {
 	struct inode		*fi_inode;
 	u32                     fi_id;      /* used with stateowner->so_id 
 					     * for stateid_hashtbl hash */
+	bool			fi_had_conflict;
 };
 
 /*