NFSv4: Replace lock_owner->ld_id with an ida based allocator

Again, We're unlikely to ever need more than 2^31 simultaneous lock
owners, so let's replace the custom allocator.

Now that there are no more users, we can also get rid of the custom
allocator code.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 8d1739d..df60d99 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -1093,6 +1093,7 @@
 	}
 
 	ida_init(&server->openowner_id);
+	ida_init(&server->lockowner_id);
 	pnfs_init_server(server);
 
 	return server;
@@ -1118,6 +1119,7 @@
 
 	nfs_put_client(server->nfs_client);
 
+	ida_destroy(&server->lockowner_id);
 	ida_destroy(&server->openowner_id);
 	nfs_free_iostats(server->io_stats);
 	bdi_destroy(&server->backing_dev_info);