NFS: Ensure that we always drop inodes that have been marked as stale

There is no need to cache stale inodes.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index e12cea4..aa5315b 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -308,6 +308,7 @@
 	.alloc_inode	= nfs_alloc_inode,
 	.destroy_inode	= nfs_destroy_inode,
 	.write_inode	= nfs_write_inode,
+	.drop_inode	= nfs_drop_inode,
 	.put_super	= nfs_put_super,
 	.statfs		= nfs_statfs,
 	.evict_inode	= nfs_evict_inode,