NFS: Readdirplus can't help lookup for case insensitive filesystems

If the filesystem is case insensitive, then readdirplus can't help with
cache misses, since it won't return case folded variants of the filename.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/dir.c

@@ -696,6 +696,8 @@ void nfs_readdir_record_entry_cache_miss(struct inode *dir)
 
 static void nfs_lookup_advise_force_readdirplus(struct inode *dir)
 {
+	if (nfs_server_capable(dir, NFS_CAP_CASE_INSENSITIVE))
+		return;
 	nfs_readdir_record_entry_cache_miss(dir);
 }